Tmobile lost my trade in and is not honoring trade credit.What can I do?

T mobile is doing this to my boyfriend. The entire sale was ridiculous. He went on the last day of the i phone deal with a trade In. After 6 MONTHS! Suddenly his trade in didn't qualify. Also they canceled his phones insurance and that's illegal without letting the customer know. His bill is over 200 a month know because he got a watch also. The only reason his phone didn't qualify apparently was because his find my iPhone was still active. He previously had the same phone service metro pcs and always fully bought his phone from a third party and just connected it. This was his first time actually buying a newer i phone and finally leaving METRO PCS for what i said was better service..smh. thanks a lot t mobile...  not. The sale of the phone went through 2 people..ridiculous,  because he wanted a large storage on the phone than they carried in store. So it took like 4 or 5 day to  send to our home and like i said it was the last day of the "promotion" so he was allowed to get the deal "they said" ordered his phone and let him leave with his old phone until his new came.when he went to connect the new phone and hand over his old also he was keeping his old number so that had hoops to jump, it was a complete different employee helping but he had no idea what was going on.... red flag! Well now I'm upset with the bad business practices, it feels like a scam. I'm icked with them and my bill is good. I'm leaving in a few months