Does anyone have a working contact email address for isac@fsec.or.kr?

From time to time we receive a security complaint from them, usually

involving an IP address on our network that we know is not in use.

They claim to represent the Financial Security Institute(FSI) of
Korea, and usually say they may contact law enforcement in both our
and their country. They request that we advise them of our action
in whatever matter they happen to be complaining about.

So far, so good. But...

There is no record of fsec.or.kr at the APNIC nor KRNIC.

All attempts to reply to these folks are in vain; they reject EVERY
reply message - even "hello world" - with the rejection notice that
the message contains spam.

Before I put them in my 'smtp connection refused' list, I'd like
to discuss the matter with them, or to at least let them know that
they have a severe CRIS problem.
  - Brian