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.
Step 1 of 4
Find "Cellular"
Tap Settings.
Step 2 of 4
Find "Cellular"
Tap Cellular.
Step 3 of 4
Turn mobile data on or off
Tap the indicator next to "Cellular Data" to turn the function on or off.