trying to get contract cancelled

Well it is now nearly 2 months that I am trying to get my contract cancelled and over to Pre-Paid (prepaid migration). Phoning is a disaster hang on for over 40min then get cut off or still no response. Finlay I go in to MTN once again and they help me ***. But still nothing. What is still the worst the money built up they take no refund or pay over to prepaid. Real ******* as I have paid for the minutes. Vodacom puts your left. over money on to prepaid why cant MTN