T-Mobile ID - How to delete?

I have the same issue. Might try Twitter some time soon, as I do not want to link my facebook account to T-Mobile which now seems to be a requirement to get any help on Facebook Messenger chat.

The issue with "unregistering" a formerly, now defunct, account with email is this: You can reset the password for the email and the associated account, but when then logging in, you need to attach a phone line/number. If that phone is used on another T-Mobile ID, you are told to log in with that other ID. The end.

So the phone cannot be transferred to the old email, and the old account cannot be deleted and closed. Which means that the old email remains blocked forever from T-Mobile use. Not a good user experience.

I appreciate that at least meanwhile one can link multiple prepaid and postpaid accounts under one ID&email. The administrative division between post and prepaid was the biggest downfall of T-Mobile for the longest.