If you want to avoid using data, you need to deactivate data connections on your mobile phone. Once done, you can only make voice calls, send SMS and use applications that don't require an internet connection.
Step 1 of 4
Tap the menu icon.
Step 2 of 4
Step 3 of 4
Activate or deactivate data connections
Tap the field next to Mobile network to select On or Off.