Even though this sucks, I want to remind you of the story of nissan.com, which is at least one point of data showing that the name oversight organization (I forget their acronym just now) will not bow to pressure, even from enormous, multinational, moneyed corporations with huge brand recognition. I also want to reiterate what the other commenter said about suing. You can't let them operate under your brand name, or that can be used as granting a kind of defacto permission to use the name. I hope things work out for you.
Also, even if you remember the story, visit nissan.com for possibly some useful information for your situation. Good luck!
Also, even if you remember the story, visit nissan.com for possibly some useful information for your situation. Good luck!