Excessive data charges in last 2 months of contrat

Vodacom have charged me over 3k in the last 2 months for excessive data usage on my phone, I on average use 1.7GB of data a month and now in my March account I have been charged for excessive data amounts, two events which cost R900 each, Vodacom eventually sent me the report after I have to resort to facebook to get any service, now I haven't received any response since replying to the feedback. This month I have turned my cellular data off completely and int he last two days i only allowed whatsapp to use data and I still only turned it on when needed, I got an SMS that i had no more of my 200MB data left, so turned off the data, bought a new bundle and only when received confirmation it was activated did I turn it back on. Now I see online I have been charged for /- 30MB of data not even in a 1 minute period, then looked at my balances and I still have data left from the previous bundle. Just shows that Vodacom charges what they like, when they like. I'm disgusted in their lack of service!