Vodacom do not listen

Hi, I am trying to cancel a contract, but the agent keeps trying to to get me to renew it with specials. They will not listen and honour my request. I am then told after being on a call for nearly 30 minutes, that their system is down, and that they will call me back when its up again. I told him to cancel it, so what is so hard about that. I no longer require that particular service and just want it terminated as its in the last month of the contract.