Vodacom contracts *****s 1

Vodacom agent came to my house to sell me a data contract where I signed for a month to month contract. On the same day of the installation I called Vodacom call center to activate my contract I found out that I am signed in a 12 month contract which I did not sign for. And they denied to fix it telling me that I have to cancel the contract and pay the money for canceling.