If you need to dispute a payment made with Facebook Credits, there is a system with Facebook you can use do to this. Please follow these steps to get the correct contact page.
1. Load the Happy Aquarium page.
2. At the very bottom of the page, click on Report/contact this application
3. Observe the dialog box, pictured here
To raise a ticket about a Facebook Credits purchase, choose the third option. On the next screen, you can select the transaction.