Great! You can process your payment thru T-Mobile app, that way you can avoid being charged the $10 payment support fee.      

1. Open the app.    
2. Tap BILL.    
3. Scroll to and tap Make a payment.    
4. Select the amount to pay, the date to make the      
5. payment on, and the payment method.    
6. Tap Agree and Submit.

https://www.t-mobile.com/support/account/pay-your-bill