Ridiculous card billing on closed account

I had a Nedbank credit card account in 1998, that according to me was paid and closed, but now that I am trying to buy a house, to my surprise I am listed on ITC for an account with Nedbank that is long forgotten.I tried to contact the legal department and to date it is now 5 months that I am trying to sort this out with NO reply from Nedbank No emails received as promised by the customer care department. NO information anyone can give me on that account, BUT YET they list me on ITC , they ask me for proof of payment when it should be on there records that no money is outstanding and that the account was closed. NO one is willing to assist OR do ANY effort to investigate this issue. They want me to settle a bill of R11 000 in order to clear my name, for money owed to them, that I don't even know of. I have never been treated so badly EVER. How can I give documentation if I had a personal banker working with my accounts and that I trusted HER that the accounts was closed. I am sooooo frustrated and Nedbank just do not give a damn