MTN failed to cancel mycontract

I contacted MTN on the 6 of October to cancel my contract that was supposed to expire on the 29th of October as i was informed that the contract should be cancelled 20 days prior the end of contract. I was told that the phone that the Retentions Department will be in contact with me for the cancellation and migration of my number to prepaid. I did not received any feedback from them. on the 21st of November i received airtime and sms from mtn then i called to inquire why am still getting airtime where as the contract is cancelled and the told me that my contract is active and that they will assist me to cancel . On the 26th of November MTN debited R599 from my account and wen i inquire they told me is the money that remained from 2013 when i upgraded my contract. On the 24th of November i receive an email from retention that my contract Will be cancelled and my number will be migrated by the 20th of December 2015. on the 21 December i received airtime and when i ask the consultant told me that my contract is still active.<br> Please help me with the cancellation asap .<br> Thank you in advance : Mokgadi