New phone trade-in credit

Mid-October I ordered 2 new iphones for existing lines on my acct. Upon sending in my old phones, I was to receive a $700 trade-in credit -- applied monthly for 2 years. I sent both phones in. Per USPS tracking, both were received by Xfinity. I received the trade-in credit for one.  The other is in limbo somewhere. I've had 4 conversations with 4 different reps. A ticket was opened mid-November, but every time I call there has been no movement, let alone resolution, on my ticket. Each time, the rep gives me a manual monthly credit and says the 'back end team' will resolve it soon. Well yesterday I was on the phone with a rep for an hour and half trying to get this resolved. She really spent a lot of time with some other teams trying to figure out the issue. They could not figure out why I did not receive the $700 as I am eligible. They said it was some glitch in the system. The resolution was for me to call in every month for 2 years to get the credit manually applied to my account -- which is an absolute ridiculous request. I asked for a check or a one-time $700 credit and neither were possible. I asked for them to figure out how the credit can be automatically applied and that was not possible. The rep really did try and I am not faulting her. But to make the customer call in every month for the credit is absurd. I'm posting this here because I am unable to find any way to escalate my issue for resolution. Hoping someone knows how I can escalate or someone from Xfinity sees this and can help.