Kim,
I remember a double refund happening before with another host.
I think in that instance the guest asked for a refund directly to the host, and also to Airbnb. The host, trying to be nice, sent a refund. Airbnb also sent a refund.
Is this similar to what happened to your reservation?
It sounds like you have been trying to get help through the normal channels without much luck.
Some hosts say that if regular Airbnb support has been contacted, but is not being helpful, you turn to twitter and facebook.
They say posting your complaint loudly there on their public twitter feed and public facebook page will sometimes shake loose some help.
There is also a twitter help line.
AirBnB Twitter: @Airbnb2
AirBnB Facebook: https://www.facebook.com/airbnb/
AirBnB Twitter help: @airbnbhelp