Reading the official documentation CallScreeningService will not be passed incoming calls if the number is saved as a contact, unless your app has the READ_CONTACTS permission and of course the permission is also asked to the user explicitly.

I’m trying to code my first test app, so I don’t really have all the strings in Android/Java programming coming from C#/PHP and others. What I want to achieve is a screening service who blocks incoming calls based on specific criteria. I know I could use many other srevices, my point is not to obtain a result but write the code to achieve it.