This is an extremely frustrating, reoccurring, intermittent issue that seems only to have temporary fixes. This has been going on for months. I have tried on Google Chrome, on Microsoft Edge, on Internet Explorer, and Mozilla Firefox to refill my prepaid account. Sometimes, it will work, but most of the time what happens is I log in, I click the "Refill account" button, and I choose credit card at the bottom of the page (choosing the other options doesn't make a difference). It loads the page, I see it for a split second ... then it goes back to the page with the "Refill account" button.
It seems like such an important issue should be addressed sooner. I have talked to support several times and they always, always tell me to just try a different browser, and it only works 1/10th of the time. One tried to get me to tell them my credit card information in the chatbox by the way. I like Tmobile, but I'm very close to finding a company who has a working website instead.