Extreme weather conditions are always VERY difficult. Add in the fact that most flights are going out FULL these days and you have a very big mess. DL probably didn't have any flights to book you on. That being said, they should have looked at their partner carriers, CO and NW, for help.

Customer Service addresses are best found on the airlines' own websites. Just click on "Contact Us" and usually the addresses will be found there. Or call and just ask for the address for customer service (refrain from explaining why).

Also, if you had access to a computer, sometimes you have to do your own research. See which airlines appear to be operating and make suggestions. Unfortunately, the phone agents have less power to change your reservations than the airport agents. Also, you may have been dealing with the commuter carrier's airport agents (which tend to be much less knowledgable than the airline's own agents).