Harassment and Abuse

I used to be Direct v customer in 2008 to 2010 due to over charging a dispute came and i left direct v ....i  to a new house ,,,,and in 2014 i signed in with att for wireless account .Yesterday 09/20/2019 I went att store t to buy and get two smart watches ,but the sale person told me you can not get because you owe direct v $486.00 , I tried my best to call all possible Att  direct v number  not one could give me rite answer, This my second day to reach rite department  .....I even do not know the name of collection agency., I have no clue what to do....Please help me I am a disable person ....Thanks......Farooq Choudry   tel:4*******************6 my email address is F**************************@***************