Vodacom changing prices of bundles without approval of customer????

I received an sms a week or so ago to tell me that the prices of certain contracts are changing and so are the offerings (in terms of data and minutes etc) with effect from May 2018. When I clicked the link I saw that my bundle is changing in price and offerings. I have NOT In any way agreed to this, no one has called me and neither am I interested in the increased price OR offerings. I am perfectly happy with how it is now. How can you just change prices without the consent of customers. I am not prepared to, come May, suddenly pay increased prices. I refuse to as is my right as a consumer