oops technical error

I've have tried to upgrade my phone. was formerly a sprint client then they merged. every time i go to check out for a new phone it pops up oops technical error. I spoke to T-Mobile and they said my card would go through. I spoke to my bank and everything on my end is fine and when they tried to charge my card on mobiles' side it was 3 times for zero dollars. the bank said its on their end with their system. I told the T-Mobile person this and they said no its not. quite fed up with the bs company.