Vodacom contact changes

On the 2nd of May 2023 I upgraded my contacts and was quoted a package and an amount I was to pay for the next 24 month period. On the 1 June 2023 I received my bill only to find that the amount was not the same as the quote sent to me and accepted. I immediately contacted Vodacom customer service, and was told it would be sorted out. After waiting a few days and seeing that it had not been resolved I contacted them again and was sent from one department to the other without the issue being resolved. I have now been told it is because there was a price increase and I should be happy a I have been put onto another package that costs more. At no time was I notified of the change nor did I give my consent. I have paid the amount I agreed apon, and now my account is in arrears though no fault of mine. I have always understood that a contract once agreed to can not be change without the consent of both parties. Please could you assist with this matter.