Standing Debit order changed without my consent

I have two contracts with Vodacom ,one expires June 2015 and the other November 2015. I am a pensioner so i cannot afford to let anyone take money just like that. The one phone is R135 and the other R149. Suddenly i get an invoice for R343, no upgrades, no nothing yet item codes are changed magically and the R135 is now R194. How is this possible as i am the account holder and requested nothing new. Vodacom is definetely on my list of to get rid of asap, as i have continuous problems with them, and its always the accounts dept. So can anyone explain this breach of contract, needless to say i will be contacting my bank to allow only the R284 per month debit, and if not rectified by vodacom i will take it up with the consumer council.