If you want to avoid using data, you need to deactivate mobile data on your mobile phone. Once done, you can only make voice calls, send SMS and use applications that don't require an internet connection.
Find "Mobile networks"
Turn mobile data on or off
Slide two fingers down the display starting from the top edge of your mobile phone.
Tap Mobile networks.
Return to the home screen
Tap Mobile data traffic to turn the function on or off.
Tap the home icon to return to the home screen.
*Please refer to the Sony website for more information or further support.*