Cancellation request declined

My cellular contract ended on 18/03/2015. I've been to the MTN stores several times since then to request the cancellation of my completed contract. However, every time I request to cancel the service the representatives advise me that I need to contact the Customer Care help line who I never get through to. I've been trying to contact them every single day since I've been advised to do so but whenever I make the selection to be passed to a consultant the system disconnects the call. I advised the stores about this but all they could say was I have to keep trying. I'm not too sure how long exactly MTN would like me to keep trying as trying doesn't really get me anywhere. MTN is charging my account every month for a service I no longer need and what I have requested to cancel. They are very quick to lock you into a contract but close the doors on customers who would like to cancel the contract after completion and hold them liable for all charges. ABSOLUTELY BAD CUSTOMER SERVICE AND I WOULD NOT RECOMMEND MTN TO ANYONE AT ALL.