Cell C legal Department. What is this?

The Home Connecta Flexi Prepaid was suppose to be a deal entered into on buying a sim with cell c. At time of purchase tarrif was great. Now I find that tarrifs for data are changing and the offers are ridiculous. And to note that the terms of conditions have changed regarding the offer and the offer expiry date has not been reached. Is this even legal. I have read the terms before posting this and cell c has the right to withdraw the offer at their discretion not change the pricing of the deal as long as the deal is available. Now I bought airtime to buy the R189 for 40 gigs as it was available the 17th of March 2022. The terms read also that if their are changes customers will be informed. The data deal is not available no notification has been received. Legally what can be done. Thanks