Vodacom Cancellations never cancel

I paid up my contract in store but could not cancel it. Had to phone a cancellations dept. Phone and cancelled. 3 months later I get an invoice. Rep**** on the mail and got a call from a cancellation agent who says the request wasn't carried through. Asked her to cancel it and she said she can't due to outstanding invoices. She spoke to her supervisor, who said he would cancel it to prevent further charges. Was suppose to get a confirmation email and sms (still no confirmation). Again I get an invoice and respond, to which they say the cancellation wasn't carried out. This is affecting my credit rating and I am not happy that a simple thing as a cancellation can't be carried out at a store (to be sure that it is done). Vodacom please sort this out....