I had 200+ usd left in my gophone account (expired date was Feb 21, 2014). I'm working in Thailand and will go back to US in April 2014. I tried to add credit several times but failed to login on my account. Can't not make an international call from my prepaid Thai phone. No AT&T email address to contact. Finally, I suscessfully added $100 to my gophone account today. Just found out that $200 were gone.
The $200 remaining in your account balance has been forfeited due to exceeding the set expiration date. Unfortunately, there is no way to get it back. This was stated in GoPhone's TOS upon the activation of your service.
You could try to reason with AT&T once you return back to the U.S., but they will likely tell you the same thing. In the meantime, there only other way you would be able to contact AT&T is by submitting a private message here: