How to totally block internet access (data) on an Android?

I use Android 4.1.2 dual SIM, so I often switch SIM cards and restart the cell phone.

My plan allows me internet connection, but it's pay by the day, so even if I mistakenly sent one byte, it would charge me fully for that day. Which I want to avoid!

Each time I restart the phone after I switched SIM cards, it starts connecting over the internet, although before the restart all the settings were to disable internet.

Is there a reliable way to disable internet access on Android, that will last between replacing SIM cards and reboots?

PS I do want to be able to use Wifi. But not data over my cellular provider's network.

You may suggest to call my cellular provider and ask them to disable data. It's not a good solution:

1. Their customer service agents don't like to do it.


2. Their settings seem to be reset each time I move their SIM card to a different cell phone.


3. Sometimes I do need data in an emergency.