Vodacom refuse to let go!

I thought my complaint regarding a cancellation not being done, had been dealt with. I have now received a bill for the cancelled account - I had requested that this number be cancelled as I no longer require it. It has not been cancelled - it has been transferred to Pre-paid and I have been billed. I attempted to phone the Vodacom cancellations number but the computer voice advised me that I could not question a pre-paid number. I therefore have no option but to attempt to reach Vodacom through Hello Peter once again.