Charging me more than what I agreed to

So I received an sms from Vodacom on 27 March 2015 that my contract will no longer be the amount I have signed for but now a higher subscription. After trying the accounts departments number for at least two hours I get through to a gentleman that explains that Vodacom can change my price plan because I agreed to those terms which is somehow misleading because when you sign a 24 month contract stating a certain amount due each month for 24 months. So currently my fiance and I are both unemployed and this will most likely affect all our cobtracts. I am very unhappy and I am sure many others are too. What is going on Vodacom???? No one actually gets told that Vodacom can do this! I sold Vodacom contracts and never have I told anyone oh and by the way Mr.Customer they can increase your contract amount if they want to, because then no one will sign anything, right? Very disappointed in the so called Best Network in SA.