Northern Leasing/SKS associates SKS associates is trying to charge my business account for supposedly back taxes. new york, New York

This week I received a letter from SKS Associates telling me that they were going to charge my business account for unpaid taxes that were found through a recent audit.  I used to lease a card machine from Northern LEasing but paid it off in 2009.  Now this letter is telling me that I owe money for back taxes and I tried calling the phone number provided but the rep who answered was just being stubborn and wasn't hearing anything that wasn't me telling him that I wanted to pay.  I believe this to be fraud and they are trying to steal my money as well as other small businesses' money.  Is there something that can be done because I am sure that these people are crooks who are trying to steal money.