I apologize this information showed on the bill, this code is actually an internal T-Mobile short code used for your service. These are not billable messages and do not count against your service in any way; normally these details wouldn't show on the bill and we've taken steps to ensure the messages do not show on future statements. Please let us know if you have any other questions!
Any information on what it is and how it might have started might be helpful.
Me and my fiancee got these too on our bill but nothing on the phone.