Check your Background App refresh, Location sharing, Exchange active Sync,
Use Background App Refresh
After you switch to a different app, some apps run for a short period of time before they're set to a suspended state. Apps that are in a suspended state aren’t actively in use, open, or taking up system resources. With Background App Refresh, suspended apps can check for updates and new content.
If you want suspended apps to check for new content, go to Settings > General > Background App Refresh and turn on Background App Refresh. If you quit an app from the app switcher, it might not be able to run or check for new content before you open it again.
Location Sharing How it works
The family organizer sets up location sharing in Family Sharing settings. After location sharing is turned on, the organizer's location is automatically shared with everyone in the family group. Then each family member can choose whether or not to share their location. When you agree to share, your family members see your location in Find My Friends and Messages. If your family members have iOS 13 or later, they can see your location in the Find My app. If they have watchOS 6, they can see your location in the Find People app. And you can see where they're located too.
Exchange active Sync
If you use an Exchange ActiveSync account, it might continue to use cellular data even if you turn it off for Mail and Calendar. To see the cellular data usage of your Exchange ActiveSync account, go to Settings > Cellular > System Services.
It also could mean some photos on your device are synced from a PC/Mac
Is this what you are seeing? See the pic below
Please check the following
- Settings > General > Background App Refresh and turn OFF, Background App Refresh
- Location Services > Which app is using the "Location services" as Always and was used recently. Avoid Always.
- Sharing Location with Friends and Family Members
- Mobile Data usage, if WiFi Assist is turned ON
- Please go to Settings > General > iPhone Storage > [Check the apps which have used
- Is the iPhone backing up on iCloud?
- Is the iPhone syncing with Mac/PC over WiFi?
