FNB harrasment

How does one continuously get calls from a debt collectors, that has all the incorrect data stating the following: Your account is in arrears, yet the bank advised that your account is up to date for 2 years already. However, the debt collector's can't see what the bank sees. 1 + 1 = 2 simple. Yet the debt collector/attorney continues to harasses you. So do I play Mr. Evil and lay a case against the attorney for harassment and deformation of character?

Please advise me on the way forward, FNB the number 1 innovative bank?