An ounce of follow-up is worth a pound of cure.

You just found out your credit or debit card info has been used by someone else to make a fraudulent purchase. There are so many different people you can call, each involved in some aspect of this theft. There’s your bank that issued the card, the credit card network the issuer uses for that card,…

via Who Am I Supposed To Call When My Credit Card Info Is Stolen? — Consumerist

Work with your bank first and foremost and do it immediately. Time is not on your side when disputing a fraudulant charge to a credit card. Once you got the wheels rolling with your credit card issuer, at the very least add your incident to the FBI list of Internet Crimes. They may not investigate  your individual incident but use it ganged up with others to link related incidents. If they don’t know about  yours, they may not have enough info to link up. So at the least report it to the FBI too. Then take necessary precautions to protect your personal identifying info.