If I can plug an app I found helpful in reducing robocalls: Try RoboKiller (iPhone, not sure about android).

I tried Mr. Number and a couple other free options which didn't seem to block much. I paid $30/yr for RoboKiller and unwanted calls have been reduced substantially - to maybe 1 per week slipping through. It's not just doing caller ID analysis, you actually forward your calls to them and they screen them before they even get to your phone. Seems to work well.