Promotional Trade-In Credit Never Applied to Account?

I am on the same boat . After several follow-up with customer care representative, one of the supervisor talked to me saying he will check with backend team and call me back with update. When I called after a month, customer care representative told that there is comment in ticket from supervisor mentioning promotion code could not be applied and they refused to transfer the call to  supervisor. Now I regret my decision of moving from ATT to T-Mobile.