Vodacom unauthorized travel data

For the second month in a row, Vodacom just add over R1000 of travel data to my bill. I did not buy it, I didn't ask for it, I don't use it, yet they one sided just add it every second week to my account while I am traveling. No matter what I try to do to stop it, they simply refuse. I can call. Submit a request to stop it, but they simply hust keep on increasing the amount. So, when I am back in South Africa I will definitely tell them what they can do with their So called contract.