The app simplifies Android’s built-in ability to block contacts from calling, so a contact has to be created for each blocked number. We tack zz_ onto them to ensure they stay pinned to the very bottom of your contact list.
Another option, if your phone’s implementation allows, would be to create a contact group for those numbers, and then have it hidden from your main contacts display. This is phone dependent so we can’t provide specific support for this option.