Data being used even on WiFi? Data Sense claims it is

[Gabranth]

And yes that checkbox to have wifi always on is checked off...

You should checked that box.
It will keep the wifi on even while the screen is off.
If not your phone will turn off Wi-Fi when the screen is off, and if you downloading Big appsor something it will use your cellular data.
Combine with Wi-Fi sense your phone will automatically connect to free public Wi-Fi like Starbucks

 

[Dr Love PhD]

Nnnnooooo, phone calls are unlimited. You will only miss mms. I do not have a data plan and use wifi 100%. Actually, I'm on a pay as you go to avoid paying for cellular data.

 

[lucas.scott]

Its a long shot - but we see similar problems with customers all the time. A common culprit of spiked data usage can be an email stuck in "sending" status. As soon as you leave a wifi area it begins chugging at your data all day every day.

Its a small shot, but worth looking at your sent folders.

 

[Zacharyw70]

there is an option in the wifi settings that keeps wifi connected even when the display is off

if that box is not checked then your phone will revert to cellular data every time the screen goes black

Where's this located in WP8.1 if it's still around? I can't find it.