Inept call centre staff - migration to prepaid

After numerous calls to move to prepaid now that my contract has expired, I get conflicting information and promises from the MTN call centre, but still have not been moved to prepaid, instead my contract has been kept active and incurring monthly charges. What is so difficult about this? Surely a common request. Please cancel my contract immediately, refund the additional charges for the month after I had requested being moved to prepaid.