Cell Phone Number Hacked & I Need to Fork Bill

Billed over R1,100 for data charges on a cell phone account I don't use. There was data purchases made through Vodacom's mobile APP, which I don't even have installed. How secure and safe is your mobile APP Vodacom if someone was able to buy data on my account, without me been aware of it!!! The sim on the account has now been blocked but I am still liable for the costs even though its you Vodacom that has mobile APP that clearly has security flaws.<br> <br> I would like to know Vodacom what you intend in doing!!!