Contract changed without both parties' permission

I have two contracts with Vodacom. Have had them for years. The one for almost 15 years. A few months ago the contract amount was changed, in the middle of the contract period, without even discussing it with me. I accepted that I had no choice. But found out today that it is completely against the CPA. I would my contracts returned to the original amount, as well as a refund for all the moneys that was *******ly claimed from me.