You can avoid unintended data traffic by deactivating mobile data. No connection to the Internet via the mobile network can then be established. You can still use WLAN even though mobile data is deactivated.
Find "mobile network"
Press arrow right to access the main menu.
Press mobile network.
Activate or deactivate mobile data
Press the indicator next to "Data connection" to activate or deactivate mobile data.
Return to the Home screen
Press the Home key to end the session and return to the Home screen.