Turning off calling restrictions iPhone 11

It sounds like someone has placed restrictions on your iPhone.

Check Settings > Screen Time. Or perhaps your iPhone is governed by a school or employer. Or perhaps you have an issue with your cellular carrier.

Are you seeing this message when dialing someone you want to call? If you are, it's on their end, not yours. It most often means there is an issue with their cellular service. You can't fix something which is on someone else's end.