Can't log in super users created on the django admin backend

I'm trying to create superusers on the django admin backend, but somehow I can't get them to log in. Here's my user class,

class User(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(unique=True, max_length=255)
    mobile = PhoneNumberField(null=True)
    username = models.CharField(null=False, unique=True, max_length=255)
    full_name = models.CharField(max_length=255, blank=True, null=True)
    is_staff = models.BooleanField(default=False)
    is_superuser = models.BooleanField(default=False)
    is_active = models.BooleanField(default=False)


    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = ['username']
    objects = UserManager()

Here's the UserManager function to create super user,

def create_superuser(self, email, username, password=None):
    user = self.create_user(
        email,
        username=username,
        password=password,
        is_staff=True,
        is_superuser=True,
        is_active=True,
    )
    user.save(self._db)
    return user

Here's the relevant backend settings.

OAUTH2_PROVIDER = {
    # this is the list of available scopes
    'ACCESS_TOKEN_EXPIRE_SECONDS': 60 * 60 * 24,
    'SCOPES': {'read': 'Read scope', 'write': 'Write scope', 'groups': 'Access to your groups'},
    'OAUTH2_BACKEND_CLASS': 'oauth2_provider.oauth2_backends.JSONOAuthLibCore',
}

AUTHENTICATION_BACKENDS = (
        'django.contrib.auth.backends.ModelBackend',
)

# REST Framework
REST_FRAMEWORK = {
    'DEFAULT_AUTHENTICATION_CLASSES': (
        'oauth2_provider.contrib.rest_framework.OAuth2Authentication',
    ),
    'DEFAULT_PERMISSION_CLASSES': (
        'rest_framework.permissions.IsAuthenticated',
    ),
}

I'm checking the is_staff and is_superuser to true on the creation form, still nothing. The created super user can't log in on the admin backend. What am I doing wrong here.

from Can't log in super users created on the django admin backend