hmmmm....
the 'ol 'demanding money with menaces' offence
not sure if this applies in all of Oz...
but
in Vic, if someone does that and you are absolutely certain
they are wrong, get their details (name etc )
and
then tell them if they insist on continuing to demand money from
you, you will report them to the local police CIB or Fraud squad
for doing so (advice courtesy of a member of the Fraud squad here in Vic)
and
you can also report them to the licencing board
(all debt collectors in Vic have to be licenced)
tell them to send a letter 'proving the debt' and you will pay it.
If they cannot prove it...stop demanding money! (IOW..piss off)
hth
cheers