huge bills

I've been having problems with Vodacom I've put a cap on my account because of the huge bills I got every month my account is about R600 a month with a R350 voluntary cap on top of that because I can not afford these R2000-R3000 bills each month! it worked for a month or 2 they let you know when you've reached 70% and so on then soft lock it when you reach the cap. I top up my account with data so that I don't get ****** with there R2 a meg out of bundles rates. I check my balance repeatedly to not go over and out of data but get these R2000-R3000 accounts monthly with huge out off bundle megs used, and I don't get stopped and locked when I've reached my limit they just keep it going. I do what I can from my side to tray and prevent these bills it feels to my like they do what they can to make sure they get every sent they can out off us!!! will definitely be canceling my Vodacom contact as soon as i can. crazy to think we must pay these amounts every month for a phone.