Your real estate broker is sending a feed to Trulia. The Real Estate Book and some other publications send feeds. Do you have it listed with an agent?

Sorry Glenn, I should have read more. If your home is listed by someone else, contact that person/realtor.
I'd also suggest sending an email to them with your request and send a copy to yourself as well to your own history of the communications. Be sure to include the fact that you are the owner and that you request the listing to be cancelled as of a certain date.

Easy, go the service you use and list the end date. The end date can be today.