Data eaten by by VOIP gaming. 23GB over 30days!!!

I have the Vodacom 10GB wi-fi contract with another 10GB of night-owl. i usually top this up as I need it and usually do not use more than 20GB a month. This evening I was informed that I had run out of data and when I checked my data usage 23GB had been used for Gaming Void Streaming over the last 30days as well as 1.2GB for Facebook. I do not game nor do I use Facebook. I do not stream any movies, games etc and do not even use Netflix. THIS IS SHOCKING!!! If my record is checked I still have over 15GB of Night Owl data available however my anytime data is depleted. This cannot be explained as I only use my wi-fi at home after working hours and utilise the Night Owl when I am working late which is very often. Please provide an explanation ASAP this is completely unacceptable!!!