Non returned equipment fee

I moved over 2 years ago to an area that does not have Uverse. I returned the equipment via UPS as instructed. I received a letter 6 months later saying that I owed $611 for non returned equipment. I called customer service, and they said that they could see where the equipment was returned and they would credit me. Again, in 6 months the same thing happened again. I get a letter stating that they have no equipment, and that it has been sent for collections. I call again, this time they say they have a tracking number, but it isn't correct. I have called numerous times since and they have tried to credit the account and again it goes out for collection. Once again this year in May, it has once again gone out for collections. Is there someone who can fix this for me at ATT, before I close my Direct TV account and my wireless accounts in disgust and move to Verizon and Dish network or local cable? It was annoying that they sent it again after 2 yrs to collections, because I had upgraded my wife's phone (which they let me do) but wouldn't let me purchase a mini ipad at a promotional price because of this item in collection. ATT needs to get a clue about running their business. I have read at least 50 complaints about this same issue online, so at least I'm not the 1st one...