Called on 9/9/16 and did not leave a message.  Kept getting calls from similar numbers every two or three days thereafter and when I finally answered, I found out it was Comcast with an offer for me to upgrade my service.  I said that I would call them if I wanted to do something like that and I thought I was making it clear not to call back.  They called back a couple days later and I chewed them out and told them of my last conversation with them and they said that I had to specifically asked to be removed from their list in order to stop the calls (guess they don't have any common sense).  I made it clear that's what I wanted this time and they haven't called back since.