DATA DEPLETION WITHIN SECONDS

I am on a Vodacom Top up contract receiving 200MB per month. The data loaded onto my phone has been depleted each and every time within seconds. I topped up by buying data and airtime but it all has been depleted, and Vodacom has not reimbursed me with all of the money I have lost due to their network negligence (this being hundreds of rands in airtime and data). This data depletion has occurred on several occasions for the past 3 months. I have an iPhone 6 since October 2014 and I have never come across such high data usage before. My background apps are switched off since the first complaint and I also use wifi at home so the high data usage is unexplained from my side. I've complained numerous times through customer care, even went through to the data usage management, investigations have been carried out and found that my claims were correct. However, I have only been reimbursed with about a quarter of what i have loaded. If there is no feedback or reimbur*****t for the airtime lost, I would like to cancel my personal contract as well as the 10 or so business contracts I have with Vodacom. This is unacceptable.