Disput Debt

I paid off a Dillards debt in beteween my last deployment in 2005 and closed the account. Later ,after the deployment and exstension ( 2007) I got a letter from LVNV comapny saying I owed them money. I though it was a fraudulant scam.... after a while I called and found out it was for my DILLARDS account. On the phone the LVNV rep looked up the dates and amount I said I all ready paid DILLARDS and she confirmed that it was in the records that I had paid it to DILLARDS, butthat They had bought the debt from DILLARDS. Now the Department of the Army is telling me that is still showing up on my credit report. How do I getthis off? I shouldn't have to pay that company if I allready paid DILLARDS for that account.