Email sales@stardock.com as astrath noted. Unless your bank kept the funds-check hold on record, there won't be anything there since it won't actually be charged until the beta is released.
Somewhat OT, the wording is you wouldn't be charged until the final game is released; not just the beta. Not sure I'd complain either way but paying for a beta seems to be a win-win proposition without need money to be exchanged.
Back on-topic; confirmation e-mail of the pre-order should have been sent and you should be able to get it resent if you e-mail stardock. I have not noticed anything on the online account status showing pre-orders (which you think it would but anyway...)