Monthly subscription changed without notice

I have a 2 year data contract on which the monthly subscription should be the same for 24 months. The last 2 months I was billed more than stipulated by my contract. I phoned customer care and they told me my contract states that Vodacom may do this. Firstly this is absurd. And even if this is stated in the contract (which I never received a copy of), you should have notified me. I have gone through all my SMSs (of the modem device it self) and emails I have (I never delete emails) and cannot find any such notification.<br> Could someone please follow up on this!?