BILL SHOCK

So i signed up for a contract will CellC via a third party who then explained in detail how the plan works and how i would be billed for it. Imagine my suprise when 3 months into my contract my bill went from less than R200 to + R400. And i request a detailed bill - no avaial. I phone in - they just tell me its pro rata rates. Keep in mind i am 3 months into my contract. This is so messed up. I refuse to pay more than what i was informed I would pay. I have bill limit and everything setup. I even have the app to ensure that I do not go over my monthly limit. And then you speak to people who has no clue of what you talking about and puts you on hold for hours on end.