REQUEST FOR CONTRACT TO BE CANCELLED

I called MTN call centre on 15 May 2015 telling them to cancel ny contract since it was coming to an end month end and for them to convert my number to prepaid, i have the refence number for this call, i was told my request will be processed the next day. I did not use the number since it was not my main number, to my surprise a few weeks lare when i checked the balance on my phone it had money, i immediately called MTN to enquire about this, the guy that assisted me told me my account was also in arrears, i said how possible is that since the contract was camcelled according to my knowledge, he told me he has escalated the matter to credit management and that they will call me the next day, days and days went by without any call from MTN, I then called again, the lady assisting me said she is traferring me to credit management and as i write this i am still holding for credit management, for 39 minutes now, not happy with the service at all, somebody at MTN please assist me, i want this matter resolved.