Tariff Increase

So we are also one of those lucky customers who received the new popular sms saying our contracts subscriptions is going up! I taught the whole idea of a 24 month contract was to have a fixed subscription so when you choose your contract you choose a package with a subscription you can afford then suddenly Vodacom decides they can lift your subscription! I phoned a branch to get an answer as my contract is 12 years old and I cant remember the t &amp