Does the number you want blocked appear in the Blocked portion of the app? If it does not you will have to go to the Blocked list portion of the app and select the number from the list or manually enter it in. In some cases, it is necessary to tap the 'Check for Updates' button from the in app Help page to ensure that you have the latest version and all app settings are correct.
Why is Call Detector not blocking calls?
Call Detector Support -