Comcast stole my iPhone trade-in and didn't give me the trade-in value

Back in September, Xfinity ran an "iPhone 17 Pro on us" promotion where if you traded in your eligible device (my two iPhone 16 Pros), you would be credited the full amount towards the new iPhone 17 Pro. I of course took the bait after speaking to customer service assuring me that was the deal and that even though my two iPhones 16 Pros weren't paid off that I would be able to trade it in through their Elite Upgrade program because I was on the Premium Unlimited plan. For context, the two iPhone 16 Pros I wanted to trade in had device promotion credits that basically took care of the cost of the phone due to a previous trade-in I did the year before. So obviously it wouldn't make sense to give that up unless I was going to rollover the benefit of not having to pay a monthly cost for the new iPhone 17 Pros.

So, I sent in my two iPhone 16 Pros for trade-in and one of the iPhone 16 Pros was accepted and had the remaining balance zeroed out, but I didn't receive the full credit towards to the new iPhone 17 Pro. The other iPhone 16 Pro was sent back to me citing LCD damage. I thought for sure there was some sort of mishandling with the phone because I sent it in pristine condition. When I received the phone back there was no damage anywhere. It was still perfect. I guess they messed up, but now I am the one running around trying to fix it. I called Assurant and they said they can't help me and that I needed to talk to Xfinity because they would need to send me a new shipping label. I called in to Xfinity and was told to reuse the same shipping label as I had previously and that would be the easiest method to keep the trade-in mapped to my new iPhone 17 Pro. I foolishly did so, and now, even though the tracking shows it was delivered again to Assurant, neither Assurant nor Comcast/Xfinity know where my iPhone 16 Pro is after 2 months. They've already charged me $600 for the remaining balance of the iPhone 16 Pro that was rejected by Assurant and they haven't refunded me for it yet. This is despite the repeated promise that they would sort it out before it would be charged to me.

I am now on the hook for $600 for the iPhone 16 Pro plus the $1400 for two iPhone 17 Pros ($2000 total). I have 3 separate ECMs filed that show the history of my claims including what was promised to me by customer service. I haven't gotten an update on any of them. Because I am on the hook for basically paying the whole value of the iPhone 17 Pros (which I shouldn't be), I am enticed to leave Xfinity Mobile and get on a cheaper plan elsewhere, but I'm worried that I would further complicate things with Xfinity's glitchy system if I am no longer a customer. That said, what I need help with first is to sort out the iPhone 16 Pro that I sent back in pristine condition and get the $600 refunded to me. Second, I need help honoring the trade-in promotion.