2 Answers

Report it as an unathorize use to your credit card company.

Playdom is the developers of the game. 

From Playdom's page on Facebook:

If you have any issues with a Playdom game, visit our website at https://www.playdom.com. From there, click the 'Log In' button at the top right corner of the site to log in to a Playdom.com account. You will not be able to contact support without a Playdom.com account. Once you are logged in, click on the 'Support' button in the banner at the very top of the site and then the 'Submit Request' button on the right side of the page under 'Game Support'. Fill out all the information requested and submit your ticket. You should receive a reply from one of our representatives within 72 hours. 

You can create an account at Playdom here. You may need to give them the  Facebook ID used when the FB credits were purchased. http://www.playdom.com/account/login?track=organic-zendesk.com