Impossible Data usage

I have been a Vodacom customer for YEARS, I even kept my number and paid my subscriptions while I lived abroad for 8 years... And this year I have been very shocked at their service. <br> Firstly, my bill NEVER exceeds R800, EVER!!!! Yes since July 2015 I have had a few surprise bills of R3700. As a single mom I CAN NOT afford this and I know for a fact I have not used this amount of data as I have wifi at home and I am always careful. I've now just received another wopper deduction of R1382.34<br> I have queried these bills on numerous occasions but with no luck. I simply can't afford these shocking bills and don't know how to prove it can't be correct. I am on wifi 90% of the time and when I'm not, I only ever use what's app. These bills are impossible but how do I prove that. Feeling very cheated, not to mention broke! Please Vodacom, this is not right.