Personally I would go right to Marriott Corporate, explain the situation, including the unanswered requests for compensation, and then request the same (to be compensated by the hotel) from them for your troubles. You have dealt with the hotel on at least 4 occassions already, and given them ample additional opportunities to correct the situation which they continue to screw up.

Mr. Bill Marriott
Marriott International Inc.
Marriott Drive
Washington, DC 20058

Phone: 301-380-3000
Fax: 301-380-3967