Vodacom's bad service

I am absolutely disgusted with the service that I received from Vodacom. All I wanted to do was to give notice of cancellation for a data contract that will in any case expires in a months time. I don't need the service any more BUT it took me half an hour to explain to the lady to please cancel my contract on 15th January. Instead of helping me she keeps on trying to sell me more options on this contract and on my other contracts as well. As I am writing my frustrations I still don't know if my data contract will be cancelled on 15th January OR will I get another surprise next year to find out that the contract war renewed automatically. Please can anyone advise me on how to cancel a Vodacom contract by email?