It's depends on your particular credit card but most do offer protection to you for fradulent transactions. You'll have to call up the customer services line for your credit card provider and explain to them. They will send you out a form to fill in with the details which you send off. After a while, depending on the amount and how much they decide to investigate, you'll have the money back in your account.
Some may give you the money straight away, I'm not too sure but in my case with a First Direct Visa, I had to fill forms in and whatnot.