Struggling to get expired contract cancelled!!!

I am struggling since notifying MTN on 19 Feb 2015 to NOT renew my contract when it expired on 24 April 2015. As they requested to contact them the day of expiration, I am STILL waiting for my contract to go to prepaid as they did not cancel it. I have also phoned numerous times (and been cut of numerous times), and holding EVERY TIME for more than 20 minutes before someone actually responds. I have quite a lot of reference numbers already, and every time they tell me it will take 2 - 24 hours for cancellation. It has been since 24 April already!!! Every time a different excuse is made by MTN and still, there is no resolution from MTN! I want to move to another SP but can not do so due to the fact that I am still being billed and need to keep my number for business purposes. I also experience utter useless network coverage in my region. Why can't MTN just cancel my ALREADY EXPIRED contract!!! I am also told I will be notified via SMS that the migration to prepaid will be done, but you guessed it - NO SMS and NO client service. Utter *********** staff which is not able to help in any way whatsoever! Please respond as a matter of urgency as I will stop the monthly debit order for MTN