I think my experience is along the lines of this thread, they have to be connected somehow.
We have 2 Samsung S5's, an S3 & an S2. The S2 is banned from having mobile data on, so fingers crossed he's not an issue. But the other 3 have been losing 1MB at a time, 3 - 4 times a minute, random minutes through out the day. Upon studying our usage that lists the times of each transaction, it apparently started when we first got the phones - but I didn't look into it enough to see the activity, I just thought they were teens, they needed lots of data. But since December things seem to have ramped up. The phone chipped away at our data so much that my son lost 1.7GB of data in one day, all in 1MB lots. It made 1437 entries on our statement. We are still trying to work out why the phones are behaving like this and what has changed for them to increase their activity. Have switched off the feature that allows the phone to switch between wifi & data, have restricted background app activity, and have to keep turning off our mobile data after each use. Forget, and you pay. It's rampant.
I have data usage notifications in place, but none of the phones triggered these. It wasn't until our provider sent emails saying we were almost out of data - after 3 days, that we were alerted to it. I rang Samsung, who then told me that their data usage app, that monitors your data usage, actually only monitors data you physically use - ie play a video, go on FB, etc. It DOES NOT record the data consumed by background apps. So in effect, their 'data usage' app, can not be relied upon, because it doesn't mean ALL data usage.
I was livid. False advertising, putting people into a false sense of security.It's not till you get your massive bill, do you see the problem. So we are still unable to use our phones unless we are in a wifi area, and mobile data is off. We have uninstalled many apps today, and will find out later if that has made a difference. There is no way of knowing which app is doing it. Is it a factory app? I have installed Onavo, but it also seems to be showing less usage than our provider does. HELP???? In Australia.