Vodacom Price increase

Originally my signed, legal, 24 month contract was with Nashua which informed me that Vodacom had taken over its clients. I have no problem with that as long as the agreed upon contract price remains in place until my contract is up for renewal in a year's time. I've communicated telephonically with Simangele Ndlovu and Khya today, both say my contract price will increase May 1st 2015. I have no paperwork at all from Vodacom - I receive a text message monthly giving me the invoice amount which is then debited. I also contacted them via email - they responded asking for three things which will prove my identity - including a Vodacom account number - but I have never received one in writing, unless it is on those sms's. I have a one week old new phone so don't have a record of texts from before that yet. As long as my current contract remains in place I'll stay with Vodacom - otherwise I'd like to cancel it with immediate effect since they are breaching my original contract with Nashua.