No Vodacom - terrible service experience

It is impossible to cancel a contract with Vodacom - even if the contract already expired. I spent hours on the phone with the call centre, with no result. The calls just get cut off after 30 minutes or so. You also cannot hear the consultant due to the background noise. I heard the full conversation of another consultant with a customer who wanted to cancel their contract. And the consultant on that call was rude to the customer. Now when I call 082135, I am told that my number is blocked due to the large volume of calls they received from my number - probably because my Voice sim is from Melon Mobile and not from Vodacom. I am distressed as you can only cancel contracts by calling the call centre. So now what do I do?