Vodacom Bad Service

Very bad service from vodacom, all my three accounts were debited morethan the agreed monthly payment, when i went to menlyn vodacom branch i was told due to VAT increase they had to increase the monthly payment, i asked if they sent any notification, they searched and nothing was found, and i hear most people saying they recently received messages that the tariff will only be effected from May onwards from the same vodacom, i want vodacom to refund me my money as this was done without my knowledge and this was also not on my initial contracts and I also want them to send me a notification for increase before they debit my account