Vodacom wont answer my call to cancel my contract

I have tried calling the Vodacom cancellations department on numerous occasions and each time I hold for approx. 15 minutes and still there is no answer. It is unacceptable and ********* that Vodacom does not allow callers to get through to cancel their contracts . Whenever I have called Vodacom for other queries the call is answered within a few minutes, but now when they know someone is calling the Cancellations department to cancel their contract, they do not answer. I need to cancel my contract by a certain date before the contract is extended but there is no other way to do it than to call the cancellations department