Non-Returned Gateway Bill Problem

On my current scheduled bill it is including a $150 for a non returned gateway, but I have only ever had 1 gateway.   I moved locations at some point this year and requested a transfer by calling AT&T.  I was told to bring my old gateway and that I would be sent a box of cords and the guy who was setting it up at 2pm on saturday would do the setup.  No one ever showed up but I was able to set it up myself using the old gateway.  Bottom line, I have NEVER had another gateway at any point.  I called AT&T and after getting transferred a couple times I was told the billing people would be "looking into it" and to have a good day.  I have no confidence in that whatsoever and I would like to know how to get this resolved or I will be dropping service indefinitely.