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You can limit your data usage by turning off mobile data. You'll then not be able to access the internet using the mobile network. You can still use Wi-Fi even though mobile data is turned off.
1. Find "Mobile networks"
Slide two fingers down the display starting from the top edge of your phone.
Press Mobile networks.
2. Turn mobile data on or off
Press Data connection.
Press the required network or Off.
3. Return to the home screen
Press the Home key to return to the home screen.