Here is what I found in less than a minute by using the Google search
engine:

Gerd Klauss, President and CEO
Frank Witter, Chief Financial Officer
Steve Keyes, Director, Corporate Communications

Address: 3800 Hamlin Road
Auburn Hills, MI 48326

Telephone: 248-340-5000
FAX: 248-754-4930

Don't bother with lower level officials. Go to the top.

Send a typed snail-mail letter to one of the above company officers
(preferrably the CEO) and do not use email, which tend to be ignored. In the
letter, provide as many details as possible, and back it up with
documentation. Do not be insulting or threatening, that will just destroy
your credibility.

In the end, if you cannot get satisfaction you may have to hire an attorney,
and their fees on contingency cases are normally 33 percent or more of the
award.