Contact your credit card company immediately. I'm sure they will sort this situation out for you, they are usually brilliant when people have been ripped off. If you can prove you paid for the tickets on your card, the gig was cancelled and you've not had the money put back on your card, there is no question you'll get a refund. If you don't get it from the promoter you'll get it from the credit card company. What a joke.
let me know how you get on,
flairville@aol.com