What type of account have you signed up for?
Hey jonandkrystal! Just checking in with you to see if you still had concerns about this. Certain plan types don't allow for short codes, but others do - if you let us know what type of plan you have, we can steer you in the right direction. If this has fixed itself, please let us know!
I got the same issue when replying to a 5 or 6 digit codes SMS. I have the Simple Choice plan 2.5 GB (post paid).
Have you got this issue resolved yet? I recently had the same problems... it was fine before. And I didn't even change anything on my T-mobile account at all