DATA USAGE

I've just received my account for R4000 then for R6000 from Vodacom. My account went from about R600 pm then I upgraded my phone and the account increased. However we've only noticed recently that the account escalated to R2000 before hitting R4000 then R6000. HOW ON EARTH DOES MY ACCOUNT INCREASE TO R6000 pm when I am doing anything remotely different on my phone. I upgraded my phone not my account and the consultant offered me a deal to pay an extra R100 for additional data. How on earth does my data usage go through the roof to R6000 pm. Vodacom you need to investigate this urgently. I am not paying for this. I am very upset about this and it needs to be investigated.