If notifications are turned on, your phone will use mobile data when applications send push notifications and is not connected to a Wi-Fi-network.
Solution: Turn notifications on or off
1. Find "Apps & notifications"
Slide your finger downwards starting from the top of the screen.
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press Apps & notifications.
Press the required app.
Press the upper indicator to turn the function on or off.
Press the Home key to return to the home screen.