New SIM card Detected ERROR - email not retrievable

Updated iPhone yesterday- lost connection to Att.net email account. No matter what device or browser I attempt to log in from, it ask to verify my identity by sending a 6 digit code to my cell. Code is sent, I enter code, then error message appears... new SIM card detected. Try choosing another mobile number... you cannot change the method of two factor identification... it is a loop all over again.

ATT cannot seem to help either..... The kicker, I use the email for most apps, without having access to the email, I cannot access apps on my new phone. 

Can someone please message here if you have found a work around... don't tell me to try another browser, device, changing passwords etc.... all avenues have been exhausted.