Vodacom refuses to cancel the contract after years

I had a contract with Vodacom of which I regret to date. They do not want to cancel my contract, I asked to have a paid up letter and requested to close the account but to my surprise there was no communication with me I found out I'm owing them. I told them I lost the simcard, they are still billing me and not even have the decency to call me and tell me I owe but rather take up action against me. I'm so mad