Django : the page refreshed when i click on import file and no message appears

i am working on a django powered web app, and i want to customize admin view of one of my models. i have made a custom template for the add page and overrides save function in admin class to process input file before saving.

here i have the admin class of RMABGD:

@admin.register(RMABGD)
class RMABGDAdmin(BaseModelAdmin):
    list_display = ('name', 'code_RMA', 'type_BGD', 'Partenaire', 'date_creation', 'RMA_BGD_state')
    list_filter = ('type_BGD', 'RMA_BGD_state', 'city')
    search_fields = ('name', 'code_RMA', 'Partenaire')

    add_form_template = "admin/spatial_data/RMABGD/change_form.html"
    change_form_template = "admin/spatial_data/RMABGD/change_form.html"

    def process_excel_import(self, request):
        excel_file = request.FILES.get('excel_file')
        if not excel_file:
            messages.error(request, "No file was selected. Please choose an Excel file.")
            return False
        try:
            df = pd.read_excel(excel_file)

            required_headers = ["code RMA", "code ACAPS", "Dénomination RMA", "Ville", "Adresse", "Longitude", "Latitude", "Type BGD", "Partenaire", "Date création", "Etat BGD RMA"]
            missing_headers = [header for header in required_headers if header not in df.columns]

            if missing_headers:
                messages.error(request, f"Missing required fields: {', '.join(missing_headers)}")
                return False
            else:
                # If all headers are correct, process data
                rows_imported = 0
                errors = 0
                for index, row in df.iterrows():
                    try:
                        # Process row data
                        obj = RMABGD(
                            code_ACAPS=row["code ACAPS"],
                            code_RMA=row["code RMA"],
                            name=row["Dénomination RMA"],
                            address=row["Adresse"],
                            city=row["Ville"],
                            location=f'POINT({row["Longitude"]} {row["Latitude"]})',
                            type_BGD=row["Type BGD"],
                            Partenaire=row["Partenaire"],
                            date_creation=row["Date création"],
                            RMA_BGD_state=row["Etat BGD RMA"]
                        )
                        obj.save()
                        rows_imported += 1
                    except Exception as e:
                        messages.error(request, f"Error in row {index + 1}: {str(e)}")
                        errors += 1

                if rows_imported > 0:
                    messages.success(request, f"Successfully imported {rows_imported} rows")
                    return True
                if errors > 0:
                    messages.warning(request, f"Failed to import {errors} rows. See details above.")
                if rows_imported == 0:
                    messages.error(request, "No rows were imported. Please check your file and try again.")
                return rows_imported > 0
        except Exception as e:
            messages.error(request, f"Error processing file: {str(e)}")
            return False
    
    def save_model(self, request, obj, form, change):
        self.process_excel_import(request)
        super().save_model(request, obj, form, change)

and this is the corresponding template for add:

{% extends "admin/base_site.html" %}
{% load i18n admin_urls static %}

{% block content %}
<div id="content-main">
    {% if messages %}
    <ul class="messagelist">
        {% for message in messages %}
        <li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
        {% endfor %}
    </ul>
    {% endif %}

    <form action="." method="post" enctype="multipart/form-data">
        {% csrf_token %}
        <div>
            <fieldset class="module aligned">
                <div class="form-row">
                    <div class="fieldBox">
                        <label for="id_excel_file" class="required">Excel File:</label>
                        <input type="file" name="excel_file" id="id_excel_file" accept=".xlsx,.xls" required>
                        <div class="help">Upload an Excel file with the required columns</div>
                    </div>
                </div>
            </fieldset>

            <div class="help-text">
                <p><strong>{% trans 'Required fields in the imported file:' %}</strong></p>
                <ul>
                    <li>code RMA</li>
                    <li>code ACAPS</li>
                    <li>Dénomination RMA</li>
                    <li>Ville</li>
                    <li>Adresse</li>
                    <li>Longitude</li>
                    <li>Latitude</li>
                    <li>Type BGD</li>
                    <li>Partenaire</li>
                    <li>Date création</li>
                    <li>Etat BGD RMA</li>
                </ul>
            </div>

            <div class="submit-row">
                <input type="submit" value="{% trans 'Import Excel' %}" class="default" name="_import_file">
            </div>
        </div>
    </form>
</div>
{% endblock %}

when I click import file, the page refreshes and no message is displayed as if the process file function isn't executed

from django.contrib import admin, messages
from django.http import HttpResponseRedirect
import pandas as pd
from .models import RMABGD

@admin.register(RMABGD)
class RMABGDAdmin(admin.ModelAdmin):
    add_form_template = 'admin/spatial_data/RMABGD/change_form.html'
    change_form_template = add_form_template
    # list_display, list_filter, search_fields …

    def process_excel_import(self, request):
        f = request.FILES.get('excel_file')
        if not f:
            messages.error(request, "Please choose an Excel file.")
            return False

        try:
            df = pd.read_excel(f)
            required = ["code RMA","code ACAPS","Dénomination RMA","Ville",
                        "Adresse","Longitude","Latitude","Type BGD",
                        "Partenaire","Date création","Etat BGD RMA"]
            missing = [h for h in required if h not in df.columns]
            if missing:
                messages.error(request, f"Missing columns: {', '.join(missing)}")
                return False

            imported = 0
            for i, row in df.iterrows():
                try:
                    RMABGD.objects.create(
                        code_ACAPS=row["code ACAPS"],
                        code_RMA=row["code RMA"],
                        name=row["Dénomination RMA"],
                        address=row["Adresse"],
                        city=row["Ville"],
                        location=f'POINT({row["Longitude"]} {row["Latitude"]})',
                        type_BGD=row["Type BGD"],
                        Partenaire=row["Partenaire"],
                        date_creation=row["Date création"],
                        RMA_BGD_state=row["Etat BGD RMA"]
                    )
                    imported += 1
                except Exception as e:
                    messages.error(request, f"Row {i+1}: {e}")

            if imported:
                messages.success(request, f"Imported {imported} rows")
            else:
                messages.warning(request, "No rows were imported")
            return imported > 0

        except Exception as e:
            messages.error(request, f"Error processing file: {e}")
            return False

    def changeform_view(self, request, object_id=None, form_url='', extra_context=None):
        if request.method == 'POST' and '_import_file' in request.POST:
            self.process_excel_import(request)
            return HttpResponseRedirect(request.path)
        return super().changeform_view(request, object_id, form_url, extra_context)