Does the number you want blocked appear in the Block List section of the app? If it does not, you will have to go to the Block list portion of the app and manually enter the number. You may also block a number from the Home section of the app by selecting the number.
Please make sure that any security apps you may have installed are set to exclude NAME ID. Examples of those types of apps are firewalls, task killer, anti-virus apps, and any app that is attempting to perform an action when calls come in.