Django basically doesn't delete the associate file in the model you delete. In order to automatically delete all the file when model is delete, put below code inside the models.py.

Delete Files when Deleting Models Django

from django.db.models.signals import post_delete, pre_save
from django.dispatch import receiver
from django.db import models
 
""" Whenever ANY model is deleted, if it has a file field on it, delete the associated file too"""
@receiver(post_delete)
def delete_files_when_row_deleted_from_db(sender, instance, **kwargs):
    for field in sender._meta.concrete_fields:
        if isinstance(field,models.FileField):
            instance_file_field = getattr(instance,field.name)
            delete_file_if_unused(sender,instance,field,instance_file_field)
            
""" Delete the file if something else get uploaded in its place"""
@receiver(pre_save)
def delete_files_when_file_changed(sender,instance, **kwargs):
    # Don't run on initial save
    if not instance.pk:
        return
    for field in sender._meta.concrete_fields:
        if isinstance(field,models.FileField):
            #its got a file field. Let's see if it changed
            try:
                instance_in_db = sender.objects.get(pk=instance.pk)
            except sender.DoesNotExist:
                # We are probably in a transaction and the PK is just temporary
                # Don't worry about deleting attachments if they aren't actually saved yet.
                return
            instance_in_db_file_field = getattr(instance_in_db,field.name)
            instance_file_field = getattr(instance,field.name)
            if instance_in_db_file_field.name != instance_file_field.name:
                delete_file_if_unused(sender,instance,field,instance_in_db_file_field)

""" Only delete the file if no other instances of that model are using it"""    
def delete_file_if_unused(model,instance,field,instance_file_field):
    dynamic_field = {}
    dynamic_field[field.name] = instance_file_field.name
    other_refs_exist = model.objects.filter(**dynamic_field).exclude(pk=instance.pk).exists()
    if not other_refs_exist:
        instance_file_field.delete(False)