Next phone upgrade

So I turned in my iPhone 12 to upgrade for the 14pro max and I was supposed to mail it in but I wasn’t sure how to get a label so I turned it in a one of the AT&T stores. The stores sent the phone in but for a month they said they didn’t receive my phone yet and was gonna charge me so I filed a claim but they denied it. They have my iPhone 12 that I traded in at one of their warehouse but somehow the claim is denied and earlier I called a representative and she was trying to ask if I wanted to do a monthly payment for the iPhone 12 that they received on top of my phone bill. Is there anything I can do? they basically have my iPhone 12 in at one of their warehouse but are still making me pay the because they’re denying my claim that I turned in my phone and it’s at one of their warehouse.