I would say until this has been through a court they have no right in demanding any sum's of money owed!
Otherwise they could just make up any figure (like they have). It is up to them to prove you guilty of a crime through the normal legal system before they can demand any type of damages.
Not sure where you or they are from but if that's across borders it's unlikely they would pursue that route. I would personally send them a letter explaining the circumstances if they still play silly buggers ignore them after that.