Phone trade in not applied to bill

In January I bought a new iPhone 16 on the xfinity website. When ordering online I filled out the trade in information to reduce my monthly payments by $500 over 24 months. At the end of the online checkout process there was no trade in reflected on my new purchase agreement. Even though I had entered the IMEI number and provided all the correct information. I went in to multiple xfinity stores and they told me the website must have messed up my order. They told me to call customer support since I bought it online. I have been going round and round with xfinity call center personnel for over 6 months now. They just keep passing me off and nothing ever gets done. They always assure me every time I call that within 48 hours I will get a resolution. I have called once a week since January trying to trade in my old device and get the bill credits to no avail. My current device payment is $66.66 per month, but is supposed to be $45.83 per month after the trade in. Who else can actually help me get this resolved???