Returned new phone

Returned the new phone on July 11. I didn't even have the phone for a week sent it back with the shipping label that was inside of the box. Called back a few weeks later and they can't seem to track it. I since called at&t at least 30 times and each time the agents told me not to worry that they could resolve the issue. The supervisor told me today that because they haven't gotten the device I was still obligated to pay the full price which is $727.62.  Thank goodness I kept my post office receipt because they don't even know their tracking number but even with the receipt they can't seem to help me. I'm so annoyed right now!!! Never again will I get an at&t phone again