I only get calling from those who's numbers are save in my contact list

I get calling from my contacts only. If any other is calling which is not in my list they always listen busy tone. But on my mobile phone shows missed call. And if I call them back that is ok. And if they call me again from the same number even I cannot save that number then it is working.

My mobile cannot have any blocked no.

No Any other known setting. And this problem start when Iphone 11 Launched. Before even cannot get calling from the save numbers. But after several updates now only have this problem.