I know how annoying those robocalls can be. You need to log into your Nomorobo account, go to the dashboard, and click on 'Report a Number', once you do that you can report numbers that are getting through the system.
Go to voicetools.cox.com , then go to settings, expand the drop-down options. Locate Nomorobo/Simultaneous Ring and turn it on. If the Noboromo phone number is in that section, make sure that you click on the little red X to remove it. Then Turn Nomorobo/Simultaneous Ring off. That should make sure that Nomorobo will not block any of your calls.