Bad review on FNB

I am a very unhappy customer with FNB. We paid up our account over 2 years ago, as we were on debt review. We have never had a phone call, never had a sms, never had a email, never had a letter in the post to say we owed them money. Now that we are clear to go off debt review we received information from FNB (ALL OF A SUDDEN) to say we owe them R6000, banking fees for an account that we have not even used for more than 2 years, and which was conducted and managed by DEBT BUSTERS SOUTH AFRICA. Now because of them, we can't get our clearance certificate.