Q: iPhone using bandwidth when doing nothing

Hello,

im currently travelling Europe and have a MiFi with me (little device with a SIM card that creates a wifi hotspot). I've been using it to connect my iPhone which I have on airplane mode with wifi on.

Since the MIFI creates a wifi network I imagine the phone doesn't conserve as much when it's on cellular data (it doesn't know it's on cellular), however I'm using an insane amount of data doing nothing.

I have shut off background app refresh, turned off iCloud Drive, turned off push, set all accounts to fetch manually, disabled all notifications, and disabled all widgets in notification centre. However, I'm still using 1MB/minute when the phone is sitting idle with all apps closed. (Confirmed using the meter on the MIFI and with 'my data mgr' app)

i cannot figure out what the data use is from, but need to get it to stop. Any ideas would be appreciated.