Trade in - 5 months and still waiting for credit

I traded in 2 iphones in late September for the $1000 credit each once they were received. I mailed the phones which were received in October and it now has been 5 months that I have been overpaying my account. I have been charged $100 a month for both phones that I mailed and have yet to receive any credit. I have been with xfinity for years and wish I would have researched more about their trade ins as this appears to be an issue for years. I am now considering going to BBB and not sure what I can do to lower my bill. I have contacted several times xfinity and received several messages regarding that they are researching my ticket and will resolve it as quickly as possible. 

Has anyone had any luck?