A post on the Trek Facebook page is warranted IMO. I would likely write something like:
I've gotten very poor service from a Trek dealer, including work on my Madone which damaged the bike, but worse, potentially could have killed me. Trek in Wisconsin has said they would correct matters through another dealer, but now I'm not getting responses (from Trek) to my questions. I'm very disappointed; does Trek stand behind its products? To whom at Trek should I be talking to to get these serious issues resolved?
I'm sure that can be improved upon; the goal is to get them to understand that what you've been through is something that could embarrass the company quite a bit (or opened them/their dealer up to liability), but not look like a raving lunatic by (understandably but perhaps counterproductively) ranting and also not get your comment deleted by the page admins. You want to give Trek the opportunity to do the right thing and still save some face.
And then I'd follow up with a longer (emailed) letter to the president of the company. ("As I posted on Trek's Facebook page....")