cell c changes contracts without your consent.

I have had a Cell C month to month data contract for over 5 years, i recently wanted to cancel this contract and was told by the rudest consultant i can not cancel as my contract was changed to a 24 month contract. I asked why and was told Cell C has the right to change any contract when they want and that they sent me correspondence about this. I told this consultant I never received anything and didn't sign anything , I asked to speak to a manager and was told a manager will call me back and said she doesn't know when, I asked for proof of the correspondence stating my month to month membership is changing to a contract she said she doesn't have it. she then would not listen spoke over me and put the phone down, I tried to rate her service and it wouldn't log the rating. i will now cancel all my cell c sims and will spread the word that cell c has decided you don't need to sign any contracts and they can change contracts as they wish. please contact me as soon as possible.