Someone used my bank card to make their T-Mobile phone payment. How can I find out what number that the payment was payed for?
Contact your bank now. Once you know thee was likely fraud then the clock has started ticking before they do it again. In the US you have a responsibility to contact your bank when you discover a potential problem. This limits your exposure. The bank might want to change your account number.
When you talk to the bank ask them if you need to contact the police. They may ask you to contact the police depending on what their initial investigation shows.
You may not be able to get the detailed payment information, but your bank will have more information about the transaction, and have the ability to press T-Mobile for additional information.