Cancellation of contract

I've called MTN call centre three times in the past three weeks in an attempt to cancel my contract. It always takes approximately an hour for the call centre to pick up the phone only to tell you that their retentions department is unable to assist you due to technical problems and that they would call me back. To date I have not heard anything from the retentions department and it feels like MTN is holding a gun against my head insisting that I continue with the contract. The branches are unable to assist because only the call centre deals with cancellation. For a big company like MTN a technical problem for three week is unacceptable especially if they don't honour their commitment to call back. They can't resolve a simple issue of debit order not going through this month. Utterly disappointed.