they get your name by you or someone in your family entering some competition
then its pressure calls..i always confuse them by saying sorry you have the investigation department here..then you take over the conversation by asking their name, address,their personal details....they soon put the phone down
any name or address's or phone numbers you give out online somehow they have access to it..dont give out any personal detail unless you no for sure who you are talking to..don't let it worry you...next time you get a call and you dont no who it is..you ask the question and their personal details...there soon hang up...have a happy day