Hello i need to change region country on mu iPad to Region Srbija. Srbija-Serbia(europe) is not the list countries. Thank’ Best regards

If your region is not specifically listed, you may need to select the nearest region that is available from the list. I note that "Serbia" does appear in the list of available countries.

Settings > General > Language & Region > Region

If your iPad is not working as expected, try Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Otherwise, you might be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.

Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

I'm not sure that I fully understand your problem - as there are no region-specific settings for either iMessage or FaceTime beyond those already outlined.