Still debiting me even though I switched to prepai

I had a contract with MTN that had expired. I was due for an upgrade and decided to move to Vodacom because of their better service. I phoned MTN and they said I was on a month to month basis and could change to prepaid at any time without incurring additional charges. Vodacom said that this was the preferential route to go through as it would be easier to obtain the phone number. The staff at the MTN call centre said that by moving to prepaid when I was already on a month to month contract basis would mean that I would not be debited any more and would not incur any cancellation fees as the contract was up. This was back in Jan and MTN is still charging me!<br> I tried to call the call centre but I can't sit on the phone for 30 mins! I've sent an email but waiting for a response. This is why I moved to Vodacom in the first place.