Difficult to cancel MTN contract

I have a MTN contract that expired on the 21/09/2017 and on the 22nd I tried to contact the MTN call centre to cancel my Contract. I was not able to phone their ********** from my office phone so I was forced to use my cell phone. When I contacted the call centre I did not wait long for the call to be answered but then they had to transfer me to their retentions department where I waited for more than 15 minutes without any answer. I ended the call and phoned back to the switchboard and told the person that I do not want to speak to someone from retentions and all I want is my MTN contract to be cancelled. The switchboard was not able to assist so went onto their website and requested MTN to contact me. I went onto their website twice to request them to call me, but still received no call. MTN is still currently debiting my account for the full amount and it feels like I am stuck with this contract.