How to block unknown callers on Android phones
The screenshots from the original post are no longer available; the steps below are complete.
Truecaller does not block all unknown callers, it just warns you and blocks only those who have been explicitly blocked by you.
Here is an easy method to achieve it:
Step #1: Go to Google play store
Step #2: Install Contacts by Google LLC
Step #3: Now open Contacts App on your mobile phone and go to Top Left “Hamburger” Menu (with three horizontal lines) & then go to settings.
Step #4: Now go to the “Blocked Numbers” at the bottom of the menu
Step #5: Enable “Unknown”. This will block calls from unidentified numbers. You will get calls only from numbers that are in your contact list.