Why can't I receive calls from numbers outside my contact list?

[odlawalli]

I cannot receive calls from numbers that are not in my Contact List even though I have not made any changes to the phone's settings to bring this about.

 

[Tim1954]

Settings can "slip", and any updates can change them also.
Go back into the calls settings and make sure you haven't got "block unknown callers" ON...

 

[B. Diddy]

Welcome to Android Central! Which phone? Is Do Not Disturb turned on?