Beneficial / HFC Bad report after Payoff Elmhurst, Illinois

I paid off the account, by statement and on line information. With no justification or documentation provided or indicated on line. they now report that I owe an increasing amount and are reporting it to the credit bureaus. After repeated calls and a vastly frustrating voice response system I get a referral to a street address and a fax number. There has also been no response to a demand letter sent from my PPL provider attorney. But the amount they want keeps growing as shown by the credit bureaus.