T-Mobile not crediting me with service after paymnet made

I have pre-paid service and before it expired, paid for another monthly service and while the payment is sitting in my account, they have not applied it to my phone so the number doesn't work. The staff/reps on text tell me to call an 877 number but since they have not credited me the payment, I cannot call out nor receive calls in. What the heck kind of service is this? How have you been able to reach out to T-Mobile to get the money you have paid applied to your accounts without having the ability to call them. I am overseas so cannot walk into a T-Mobile. Nor can I call as I explained.