Iphone data usage

Ive just signed my mother up to 1p mobile and although she has been at home all day and on WiFi I've noticed she has been using data ( not a lot but still seems strange). I have switched off WiFi Assist already but still the same. Its an Iphone 8.

Any suggestions?

Ian

If you go into Settings -> Mobile Data the scroll right down to the bottom and click 'reset statistics'

Then leave the phone for 24 hours, come back and see what has been using data (including System Services which you can drill down into more as needed)

Make sure you have 'WiFi Assist' turned off in Mobile data settings...

Make sure you have switched off Mobile Data for all but essential Apps.