Vodacom cancelation department inefficiency

2 years ago I canceled my vodacom WI fi contract instead of renewing it. I followed the correct channels and received confirmation that the request was logged, then i received one that said request was resolved then i received one that said request was closed. The wifi was switched off on the cancelation date and the last debit order went through and that was the end of it. NOT TO BE!!!!!!!!! I started receiving phone calls last year that I owe vodacom money. I forwarded all the emails I received and the accounts department said they would sort it out. In the last 2 weeks I have received 4 phone calls from vodacom saying I owe them R9000. How the hell is that possible. No. 1, I never renewed the contract, no. 2 the final debit order went off. No. 3, the services were switched off 2 years ago. Everytime I speak to them, they promise to resolve the issue. Clearly someone is not doing their job. I am writing this here now in the hopes that someone will resolve this once and for all and offer an apology for the harrasment I have been receiving. If I have no success through this channel, I will have no choice but to report this to ICASA.