Impossible Contract Cancellation

I have a month-to-month contract with MTN which I would like to cancel and then have my number converted to prepaid (Pay-As-You-Go). I have spoken to the Cancellations/Retentions department over the phone and have sent numerous emails requesting this cancellation over the last few weeks. I have not received feedback as to when the contract will be canceled and when the number will be converted to prepaid. The request was submitted almost two weeks ago and my number is still not on prepaid. I have two reference numbers: *** & I-***. I am quite shocked by the level of service I have received and would like assistance/feedback as soon as possible. A letter confirming the cancellation and balance of R0.00 is also required.