adding users problem

adding users problem

First question -
I try to add a user (amir@experitest.com) but the system inform me that there is already a user with that Email. The Email is not in the active users, inactive users or unconfirmed users. what should I do?

Second question -
how can I make the logging in to the system with google to be disabled for this account? I have users that are allowed to access the Gmail account but not to Zoho account. What can I do?