This is a Call blocker app or an app that performs Calls screening.
Has the particularity of let you choose how to block the call, you can:

Allow - The call is not blocked
Silence - The ringtone is silenced for the incoming call
Ignore - The call is blocked but the caller perceives as if the phone was ringing, and no one answer.
Reject - The call is blocked/disconnected as if the user had manually rejected it.

It's a freemium version, without ads, you have some time to test with full functionality and inn-app purchases to remove the time constrain.

It's planned to add the ability to add individual contacts to block in a future version.
Later block numbers and prefixes.
However I think it's already useful as is, so I published it at a lower price that will entitle you to the future enhancements.

Enjoy.