As many of these calls come from call-centres on the Indian sub-continent, I have an approach which works extremely well. I politely respond to their requests, making sure I divulge no personal information, then, when they're hooked, quietly ask them if they believe in "Karma". When they inevitably reply in the affirmative, I remind them that what they're doing is illegal, brings shame on them and on their family, and will be paid for by punishment in the next life. On every occasion so far, that's when they hang up..and no call-backs...