Struggling to cancel MTN contract subscription

It is very frustrating to cancel an MTN subscription. I have been on the phone for more than 20 minutes but with no help. If I do not cancel my subscription on time, MTN will automatically assume that I want to renew it. It means I will be on the losing end of this horrible deal whilst they keep billing my account. You send me messages each other day reminding me that my contract is up for an upgrade and when I call in to cancel, one is informed that MTN is experiencing high volumes of calls. Why does it seem as if the renewal process is smooth sailing compared to the canceling process? I need help. The least you can do is to allow us to cancel our contracts at any MTN store.