It sounds as though you don’t understand how to handle user-requested deletions and when/where it doesn’t apply.
When a user signs up for your site you have the right to process their provided information (email and username) for the purpose of the registration. That processing doesn’t end when they are suspended and try to leave, taking their toys with them.
You aren’t obligated to remove the email of a banned or suspended user. The right to be forgotten doesn’t supersede the processing purpose.