Cell C changing contracts that I did not sign up for.

I contacted the call center today on 084143 to cancel my two contracts that I have with Cell C. When I signed up for the two contracts I was told that it was a month to month contract meaning I can cancel the contract at any stage, with a notice period of one month.

The lady at the call center told me that their system will not allow me to cancel because its now a 24 month contract, when I asked her about it she said that Cell C's T's and C's changed earlier this year and there are no more month to month contracts.

I am not happy about this as now I am stuck with two contracts that I don't want anymore. I was told that I could buy out the contract but this is not what I signed up for. How can they unilaterally go and change contracts as they see fit. If I was informed about this change earlier this year, I would have cancelled the contracts then and there.