Contract ammendments

I have received a message notification that Vodacom will be increasing their Contract fees. I am 6 months into the contract and feel this is a gross violation of my consumer right. I have been a loyal subscriber for the last 18 years. When contacting the Call center they just informed me that they are in their right and that it is just a business decision. How can you sponsor sports and billboards and advertise to increase your market share and then you just increase your signed contract agreed rates. I will not support the brand and you will loose another customer.