The never ending nightmare of cancelling a vodacom contract

I am so tired of Vodacom guys. I cancelled a contract and they did not cancel it. I wrote a message here they responded to say that they will give me a credit note. I received my statement yesterday and I was billed for the services. when I call their customer service and ask their consultant says my cancellation is still in process. How long is this nightmare going to last???? what does a person have to do to cancel a contract with Vodacom