Vodacom keeps delaying my contract cancellation

I am trying to cancel my cellphone contract, and the consultants keep hanging up the call twice. The last time I tried to cancel, she extended the contract instead without my consent. I complained, and the extension was reversed. Vodacom, I kindly request that you cancel the contract before you bill me for nothing. I am a pensioner now and cannot continue. There is no email address to write to.