Unable to login to prepaid account to pay bill

I have been unable to access my prepaid account through AT&T for almost 2 months now. Every time I login, I am sent to a "systems error" page. I need to access my account in order to pay my bill as my autopay has expired so I need to manually pay. Please help as I don't want to lose my account or phone number due to lack of payment. I have also tried to use 'fast pay' but that also isn't working. I am outside of the US so am unable to visit a store or call, and cannot find any email contact to message.