Hi, I moved your post over to the Casual Games forum since Big Fish is a casual game website.
When you purchase a game from the Big Fish website for the first time, there is a box you can check or uncheck stating whether or not you wish to become a Game Club member. If that box remains checked, you will be charged $6.99 per month (and any applicable taxes according to the state you reside in) and in return will be issued a game credit good for one standard game; you will continue to be charged once a month, receiving one game credit per month, until you cancel your membership. Apparently you bought a game and did not uncheck that box before placing your order; by unchecking that box, you would have opted out of joining the Game Club.
I am sure that Big Fish Customer Support will make things right for you if you have explained that you did not wish to join the Game Club; they are the best.