Brand New iPhone Return Lost in Mail

I sent back my brand new iPhone XS about 4 days after i had it.  I called up ATT first and let them know i wanted to return it, and they said to use the prepaid shipping label.  So i did.  I dropped it off at a USPS location on 9/24/18.  On 9/26/18, it said "picked up by shipping agent".  The status has not changed from that since almost a month ago.  I have called up ATT multiple times to see what can be done about this issue, and i NEVER get a straight answer.  I am not paying for a phone that i DO NOT have.  Someone please help!