They have increased the amount of money without my

I am totally not happy with Cell C's services. I have a contract phone with them that was bought in 2013 which I paid 389 for it per month. So the problem now is that, the price has changed and there was no communication that there will be changes of which I do not understand, how come they increase the price of the products they have sold already. This is my phone for goodness sake and now how come they count it on their pricing what what. the contract was for 389 not 399 and they deduct the money without my consent. I think that's *****. My contract says 24months and now it's something else. I'm so furious because they don't see anything wrong with that. I asked them and they told me sms' s were sent to inform people.