AT&T charging me 771.77 for equipment I returned on June, 28 2015!!! HELP!!!!

I am sure you do not get asked this particular question every day, but he we go. Firstly, I feel like I am getting scammed.

I have been trying to confirm the delivery of my devices since June 28, 2015 when I shipped my router, modem, and TV box through NEWGISTICS "smart label" and dropped the equipment off at UPS!!!

There, they opened my sealed package, removed the equipment, and scanned everything in the system.  I have tried going to the original UPS store where I dropped of the package and no one knows how to look up my tracking number. UPS scanned all of my Serial Numbers and there is no recorded of it every happening?? I do not understand?? The shady part about this is there are records of me calling AT&T on June 28, 2015, while I am at the UPS store, asking for my account number so I can drop of my U-Verse equipment!!!  I have contacted AT&T about this numerous times and they will not provide me with the reference number (which is included by the sender since they created the return there is some type of record) 

 I really would like some help with this issue. I spent over 4 hours on the phone today with AT&T and got nowhere. I just want to speak to someone that can help me with this issue or direct me in the right direction. A