I have had 3 of these calls I dont think you can ever stop them.
Seems to me somebody is selling names / address / phone number lists to these scammers so they can just ring up as often as they like.
As more and call centres are placed abroad (India etc) it is fairly easy for the people who work in the IT department to copy a list of the people in their customer database on to DVD and then sell it to scammers / criminals.
I would think careflluy before getting too involved. These people are criminals and if you start to upset them too much you never know what may happen.
I am not saying nothing should be done but it is up to the telephone companies, the people who "run" the interent, the police and government departments to stop this sort of thing, not individuals.
One suggestion if you get these calls is to get a loud whistle, or maybe one those klaxon horns, and blast it down the line hoping to damage their ear drums..