Why may not the Internet work through mobile data in a tablet?

Question

Android

Most recently I bought an OVERMAX QUALCORE 7023 3G (Android 5.1) tablet, bought a sim card, inserted it.
The problem is that all applications cannot use the Internet (loads, loads and then err connection timed out), but if you turn on the mobile hotspot, then other devices use the Internet perfectly through the tablet.
What is the reason for this and how can this be solved or is it better to just take the tablet to the service?

Answer 1

And you gave permission to access the Internet to them in general????