Hm, routing wars. Fun stuff. Expect much heat on this shortly...
Essentially, the point-of-appeal would probably be the IEPG
or NANOG mailing lists, and who would get believed would probably
get worked out after some protracted flameage, consultations with
lawyers, and arguments about how routing registry technologies
will save the planet from routing wars, pollution, and too-strong coffee.
My own personal advice wrt people who are thinking of using
others' address space without permission is pretty simple:
don't do it, you'll lose.