Companies can renege on contracts but customers ca

I've just been informed by email that my 2 year subscription, taken out in January 2015, is being increased. I was told by the company when the package was sold to me that the price of R99 would remain for the duration of the contact. Well, that was not the truth. Vodacom has just increased it by R10 a month. This is not a large amount when considered, but I would like Vodacom to justify how it can summarily ignore contractual agreements and just hike the price. If I as a customer decided to reduce my monthly payment, I would be seen as \breaking with my contract". """