http://41j.com/blog/2015/08/phonecall-from-a-scammer/
They did call again, I picked them up on the fact that it was a scam and asked them how they justify their actions to themselves and ask questions about how the scam works. I'll see how it goes but I seem to have got myself on some kind of blacklist as nobody has called in a month (used to get some kind of scam call at least one a week). It's unfortunate that wasting their time is the most effective defense I can think of.