Trying to Pay Previous bill

So I changed to the gophone cause it was cheaper than being on a contract and I get the same thing for lower cost.

Anyway I didn't have the money for that bill only for the prepaid now I'm trying to pay for it but I can't access my AT&T account without getting directed to the gophone account. The contact us for gophone keeps saying forbidden and when I try to email or ask support on the other site it won't let me.

Any one know how I can pay for this since the customer service line is off hours?