You've been had, Jordy.
A common ploy on unsuspecting householders.
I guarantee that these blokes will be living in some nice shiny caravans on an piece of land close to you.
You have 2 choices.
Pay £1000, tell them they are lucky to get that and tell them your son is a local Bobby......because they won't be happy.
Pay £2000 to get them off your back.....and advise any of your friends not to fall for the same scam you have.
Sorry!