Handle it this way:

1. Draft a demand letter;
2. Get on the phone and ask for a supervisor;
3. Explain the situation, get his/her name, and ask for a fax number to fax the demand letter to his/her attention;
4. Be polite but state firmly that if the issue is not resolved within, say, one month, you will proceed with filing a complaint;
5. Fax the demand letter.

This will get their attention and they'll take care of your problem.