Termination of contract

I have had an MTN cellphone contract for the past two years, when my contract was due for upgrade I did not want to upgrade as I wanted to have prepaid. A month before my upgrade was due I went into the branch where I had taken my account out and requested that my account be terminated the following month. The guy at the counter told me to phone MTN and instruct them to do so. I phoned MTN and was put on hold for 15 minutes, I phoned the next day and still was put on hold. I then emailed MTN and informed them that I want to terminate my contract, I got no reply from them. The following month my account was credited with the monthly subscription. I emailed them again saying I don't want to continue my contract and please port me to prepaid. Today I received an SMS saying my account was overdue and they would be suspending my number! I have requested repeatidly for my number to be ported to prepaid, but it is falling onto deaf ears! This is ridiculous that they just continue my contact when I have requested for it to be ported to prepaid! MTN are very quick to moan about \overdue"accounts and to suspend them"