credit card payment

I have used a credit card and on frequent penality charges opted for settlement of account. A settlement letter for Rs.4000/- was made and sent for collection. I have disagreed with the amount mentioned and agreed to pay only the amount due by me minus the wrong penal charges debitted to my account. The executive after talking to his superiors made changes in the amount in the letter and acknowledged the changes and collected the amunt of Rs. 3000/- in full settlement of account. Now, i get calls and emails informing that there is an outstanding balance of Rs.88000/- odd in my account also stating that they have not received any payments since dec, 2005. I have informed the executive who called me over the phone that the account is closed and i have a letter to that effect. The executive asked me to scan and send the same. I have accordingly replied to the email with the scanned copy. I again received the call informing that the settlement letter is invalid and therefore i need to pay otherwise he wants to report to CIBIL. What to be done ?