AT&T Mail Login & Security

The device is locked and the SIM card cannot be used

How can I get a recovery phone number set up for my email account, or some other recovery method?

I suddenly cannot access my email. For no reason, the credentials were invalid. I have literally tried everything in different orders using the information on your website. Is it possible to either get the log-in information or clear the credentials so I can start over? It is my main address and I'