Vodacom - unfair business practice

One of my many cellphone contracts was due to expire at the end of November, so at the end of October I phoned to give my one month notice. I was given a form to complete and email through, which I duly did. Now, on the 4th December I find that the contract was never cancelled. I phoned again only to be told that they had not loaded the cancellation and now they can only cancel the contract at the end of December so I must pay for another month. Very unfair business practice. This is not the first time they have done this to me so I believe this is possibly their modus operandi.