Before I ask my question - I have a Samsung Galaxy S3 4G LTE (rooted with Framaroot, great tool) with Android 4.1.2. I'm on a prepaid "voucher" plan, which basically gives you a certain amount of money you can spend on calling etc. and when you've used all of it, you have to recharge (buy another voucher with a code, which gives you more money to use on your mobile phone).
Today I made a very stupid mistake. I was using Wi-Fi at home, electricity died, my battery was low. What I did was disable Wi-Fi (through Notifications window) and checked the other settings to see if I can save battery through some other way. I saw this setting called "Mobile data" and I disabled it.
Biggest mistake ever. All my voucher money disappeared in a flash (like literally 1 second after disabling it), I'm actually still not quite sure what happened... Apparently I activated roaming or something? Boy, do I feel stupid...
Anyway, for my plan, this setting is unbelievably dangerous, it seems...
My question: What do I need to do to prevent this from happening again?
After inspecting the issue further, I learned about the so called "APNs". I have 2 default APNs, which can not be removed or disabled (directly, anyway).
If I delete them, would this block charges when disabling "Mobile data"? If not, what else could I do (besides not going near this setting ever again)?
Thanks for your help in advance.