Latest questions about "mobile data"

I was using mobile data on my phone. When it got stuck, I removed the SIM and inserted it back after a while. Now I can't connect to the Internet.

When I enable the mobile data on my Samsung S Duos, it enabled and disabled all settings automatically, even the mobile data is getting turned off.

I already activated "data network mode" but it isn't working. I can't connect to the Internet. There's no up and down arrows icon at the top.

My mobile data connection was enabled, but the connection at the top E or H or 3G does not appear on my phone. What would I have to do? I turn it on and off, but nothing happens.