Did not receive trade in credit

Not exactly sure who else to contact, I just filed with BBB today.
 I got offered a trade in for my Iphone 12 Pro Max that was paid off. It was a little more then I could sell it for, so I decided to do it. I printed off the label provided by Xfinity Mobile, and sent the phone in right away so would get my credit towards the new device they was sending me.
   That should have been the end of it. But instead I was billed full payments for the new device and no credit giving. I contacted xfinity, they told me to contact Assurant I contacted Assurant, they tell me its on Xfinity to fix, and back and forth I go for weeks. And this full device payment is on my current bill and the next again. 
 Xfinity site shows I never even sent my trade in yet, but if click on label on there site, and check the tracking it clearly shows it was delivered Sep 29th. So they have it. But keep giving me the run around.
 I've included pictures of the label they provided, and of the USPS tracking update.