Deliberate inconvenience by Vodacom

I discovered a year ago that Vodacom listed me with the Credit Bureau for a debt of R93.00 that I know nothing about. I had a Vodacom account for my daughter that they claim is the source of the debt. I cancelled that account two years ago and ported the number to MTN. Vodacom agrees that the is no way that they would have allowed the number to be ported without all the amounts due being paid. The statements were printed and there is nowhere where the show outstanding amounts. I offered to pay the amount last year already but they say I cannot since there is no invoice to pay it against but they still refuse to clear the listing. What should I do since this is inconveniencing me and has brought my life to a stand still.