Django:IntegrityError: UNIQUE constraint failed: backend_newuser.email

Question

I made custom user model in django. After creating one superuser succesfully I am unable to create new super user, it gives the error above, I don't understand the reason behind this.

models.py

from django.db import  models
from django.utils import timezone
from django.contrib.auth.models import AbstractBaseUser,PermissionsMixin, BaseUserManager


class CustomUserManager(BaseUserManager,):
        def create_user(self,email,password,user_name,about,**other_fields):
         email=self.normalize_email(str(email)); #for example ignore the case sensitivity
         user=self.model(email=email,user_name=user_name,about=about)
         user.set_password(password)
         user.save()
         return user;

        def create_superuser(self, email,user_name,password,**other_fields):
                other_fields.setdefault('is_staff',True)
                other_fields.setdefault('is_superuser',True)
                other_fields.setdefault('is_active',True)

                if other_fields.get('is_staff') is not True:
                    raise ValueError('super  user must be assigned to is_staff= True')
                if other_fields.get('is_superuser') is not True:
                    
                    raise ValueError('Super user must be assigned to is_super_user=True')
                return self.create_user (self,email,user_name,password,**other_fields)   



class NewUser(AbstractBaseUser,PermissionsMixin):
        email=models.EmailField(max_length=255,unique=True)
        user_name=models.CharField(max_length=32,unique=True)
        about =models.CharField(max_length=512,blank=True)
        is_staff=models.BooleanField(default=False)
        is_active=models.BooleanField(default=False) 
        objects=CustomUserManager();
        USERNAME_FIELD='email'
        REQUIRED_FIELDS=['user_name']