Trade in gone wrong

Hello, back in Late April I called Xfinity about trading in my iphone 17 pro for the Air, they took care of everything for the trade in over the phone and I received my email about how to trade it in with the label PDF, on May 5th I printed my label out, May 9th I went to my local UPS store, dropped off the package, I saw on my account that the phone was in “shipped” status and that was that, usually I would pay attention to the progress of the shipping but I was getting married in May so there was a lot of distractions, 2 1/2 months go by with no warnings of “Hey we dont have your package yet” so I figured it got delivered, inspected, and I saw I was receiving my credits on my bill, just yesterday I noticed I got billed $904 for “phone”, so I called Xfinity and after an hour long conversation of them looking into things they said that my trade in phone was never delivered, I contacted the UPS store, they said they dont keep records of drop offs, so I dont know what to do, that money was supposed to be for our honeymoon, im not sure what to do, I cant find my receipt since its been months, im sure there is footage of me dropping off the box at the UPS store, but Xfinity said they wont do anything unless I have the tracking number, but it literally says on my account that my trade in phone has shipped, but no other information.

Does anyone have any suggestions? I thought it was odd to that I got charged nearly full price since I got the iPhone 17 pro in September and was paying it monthly until May, I feel like I should be charged my remaining balance but also I shouldn’t be getting charged anything at all since I did what I was supposed to with my trade in