Contract dispute

I've had a very good experience with vodacom so far, has been a client since....well a very long time. The last time I upgrade was more than 3years ago and very smoothly. before the end of my contract I ran into cashflow problems and were a couple of time late. When my cashflow was restored I decided to settle my account and buy myself out of the contract. I did just that and everything was done, went over to prepaid. I didnt get any airtime, Data or anything from vodacom, had to buy prepaid. I still got an invoice every month for R0 for a yeard. Didnt bother me. All of a sudden they start sending me a bill for thousands of rand. ***. I tried to clear this up through Customer Care but nothing so far. Now they are spamming me with this Robot Call ****. Vodacom, please sort out your ****. I dont owe you anything. Someone from your side made a ****oo and I'm not going to pay for it.