Very high data costs during the night.

I got charged thousands of rands over 3 months in data costs and I was asleep when most of the billing occured.Never in all the years I've had a phone has it ever been this high.Vodacom refuses to refund me the data costs or even look into it.They are saying that it's my iPhone even though I switched off the cellular data at night after the first high bill.I have had to pay it and I really can't afford it.I cried for days and it has caused me so much distress.I feel totally **********.They advised me to download the Vodacom App and monitor my usage which I have never had to do.I always use my GPS and leave all my Apps on and it's never been this high.I don't know how to get all the thousands of rands over the 3 months back that came off my account.They do this to so many people and get away with it.