from django.db import models
from django.conf import settings


class UsersBan(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                             verbose_name="User name",
                             help_text="Choose Username"
                             on_delete=models.SET_NULL)

    ban = models.BooleanField(default=False,
                              verbose_name="Ban",
                              help_text="Users Bans")

    class Meta:
        verbose_name_plural = "Ban Management"
        ordering = ('user',)

    def __str__(self):
        return '{}'.format(self.user)

from django.db import models
from django.conf import settings


class UsersBan(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                             verbose_name="User name",
                             help_text="Choose Username"
                             on_delete=models.CASCADE)

    ban = models.BooleanField(default=False,
                              verbose_name="Ban",
                              help_text="Users Bans")

    class Meta:
        verbose_name_plural = "Ban Management"
        ordering = ('user',)

    def __str__(self):
        return '{}'.format(self.user)

Update models.py