I posted this elsewhere in this topic, but my experience with the Federal Do Not Call list was the exact opposite - they promised "within 3 months the calls would stop" and sure enough, within 3 months I never got another call.
Fair, I just checked and it looks like my number was already in the registry when they started getting worse a few years ago. (so adding it again probably did not cause the increase) You can use the site to see if you are already in, and when you were added. one of my numbers was added long before I had it.