Mobile data being charged while I'm on wifi

hatrabbit

New member
Sep 11, 2017
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I have a Pixel 2 with Project Fi service. Even with my normal data use I'm saving a lot over what I used to pay for AT&T. Still, if I see mobile data usage when I know I was at home and connected to wifi I want to try to figure out what's going on.
Yesterday I was using the Line app to talk from the US to someone in Taiwan. I was connected to wifi but was charged 9mb mobile data. The Datally app says the usage was for Line. Why would this happen? I can't find any setting that would make one app use mobile data only even when wifi is available. Any ideas where I should look?
Thanks
 
You can just pull down the shade and tap "Mobile data" and the turn if OFF.
I did that as a test for one month with Fi and used absolutely no chargeable data for that month.
I now leave it turned it on though as I like to look things up when in the car like how long a store might be open or maybe make a restaurant reservation.
Since I'm on WiFi literally everywhere, I typically only use a few dollars of data in any month.
We love Fi.