ABSOLUTELY go buy yourself a robo blocker. It WORKS. I spent right around 50 bucks and put it on our phone. You set it up to proactively block all calls unless they press a number on their keypad. This gets rid of all the robodialers. WORTH ITS WEIGHT IN GOLD. Don't hesitate. Go get one. You will NOT regret it.
Left no voicemail, but directly after this a different number called and did the same (615-657-6946). Both have been reported here multiple times. Based on that I recommend blacklisting both.