Airtime disappearing without explaination

Towards the end of August 2015 both mine and my wife's airtime was significantly depleted without any reasonable explanation. We both immediately went to the MTN branch at the Pavilion where we were given the standard excuse that we had \smart"phones that were using \""out of bundle data\"" for updates and other downloads/web browsing. This doesn't hold water because we both lost approximately R500.00 worth of airtime within the same 48 hour period whist we were at home with wi-fi access for this purpose. I have since spent many hours go back and forward to the MTN Pavilion branch to try and get answers but to no avail. My last resort is to call the 808 customer care line to request a data usage report. I no long care about this **************** that has wasted so much of my time that I will be changing my service provider as soon as my current contract reaches it full term."""