Vodacom increases costs by forcing unwanted higher value contracts without consent

I have been with Vodacom for decades, I never opposed the costs as I felt I received a quality connection. However recent increases have been done in such a way that I find absurd and should be ******* (if they are not?)! How can a business change a contract? to a higher contract and higher cost without consent?!? I receive more minutes however I do not need that!