I have a solution! (I'm exusing myself because I don't know english too well...I hope you will understand my intructions!) :)I had that problem too. So i googled like a 1000 times... I wanted to experiment with my phone and I found out how to disable mobile data to some apps... Just go to settings, than mobile data and you have a list of apps that use mobile data (skype, viber, whatsapp...)  and click one of them (example viber)  then scroll down where it says,, Disable mobile data" and similar... Click there and agree what they say and you dissabled mobile data for viber... I know that you have so many apps and that is boring but its pays off! :) Or just limit mobile data usage to 0...That works too... :)