I've started pressing 9 to ask them to put me on their no-call list, but they hang up on me before I can finish my sentence. The next time, I will play along with it and see if I can learn more.
Not only has this number called me 4 times in the last 10 days, most recent (about 10 min ago) tied up my phone - did not release, and the person stayed on the line keeping it open until I threatened to call the cops.