Every since we did the Do Not call listing our "unwanted calls" have stopped. Except for the person who had this number before us; the police were looking for him. I finally was so fed up I called the DA who had left a number on my answering machine and told this person that the previous person has not had this number for years .. She listened and made sure there were no more phone calls to our number from any police enforcement agency for the previous person.
A friend holds on the line till the call is either picked up by a human or the call ends, if its a recording (at the end of the call with an answering machine) she tells them she has their number and will report them if she has anymore -she told me that usually works for her when the telemarketers call. If its a human she tells them to take her off their listing of calls and has their number to report it.