Bridge of contract

I have a cellular contract with Vodacom and according to my knowledge my monthly installment is R250 and when I viewed my statement for this month it states R254 so I want to know why has it gone up. Vodacom is one company that is not transparent I am only binded by the Contract I would have thrown the SIM card and canceled my contract a long time ago. Communication has to be made with regard to any change in my contract