Did not receive my device credits

I switched from T Mobile to Xfinity and was promised that I would get $400 credit for one phone without trade in and $830 for my other phone with trade in. I sent in my phone for trade in credit but the credits are not showing and even when I chatted with customer service they were unable to help me out. Starting to regret my decision switching from t mobile to Xfinity specially that their network is not the best, T-Mobile used to be better.