Impossible to cancel a contract at vodacom

I have been a Vodacom customer since 1998. I found it very easy to open any vodacom contract. Yet, now that i want to cancel my vodacom contracts, it seems completely impossible.

When i visit a vodacom shop, they tell me that they can not cancel a contract at the vodacom shop. They give me a number 082 137 to phone for cancelations. For two months i phone this number, some days it just does not get answered. Other days when the computor answer and i choose the cancelation option, the computer tells me that the operator can not speak to me because my contract has not expired yet. So how on this earth can i cancel a contract which i do not want anymore, if i can not talk to an operator. It seems impossible to cancel a contract at vodacom. I am willing to pay the outstanding amount of my contracts, as long as i never ever have to do business again with vodacom.