About 6 months ago, out of nowhere, same thing happened to me.
I hadn't changed anything, but after a couple of VERY high bills, I checked my daily stats and I was at 2.3GB/day
Minimal netflix, online for work only, nothing else... 2.3GB??? EACH DAY? didn't make sense to me.
For SOME reason, Outlook starting sending and recieving in a loop, roughly 2MB every minute.
I turned outlook off for one day, usage went back down to nothing...
no changed settings, or anything. It polled the server and pulled down 2MB every minute - I'm a tech geek and I couldn't figure it out beyond that - the whole time I thought it was the ISP screwing me over (conspiracy theory) since I told them I didn't need the higher up package since I've never gone over 25GB/month.. and then is was 50-60 a few months in a row...
I never did figure out the WHY part exactly, but a repair installation of Outlook did the trick for me. Likely won't the the same for you at all, but it's hard to pinpoint unless you are measuring by appliaction and checking your usage logs yourself.
Good luck!
