I am currently in the UK and have been unable to login to my account for days (and missed a bill payment because of that!). I spent hours "chatting" to support yesterday. They reset my user ID and helped me change my password, but I still can't get into my account via the website or the myAT&T phone app.
I get error message like this, then I'm returned to the login screen:
Firefox can't find the server at myatt-doamxww00a.att.com
Opera: myatt-doamxww00a.att.com’s DNS address could not be found.
This suggests to me that there is a problem with the AT&T web site.