I've visited the official website of the developers and found out that you can buy the application with the help of PayPal. When you buy something with PayPal, the receipt including the serial license is emailed to you. I recommend checking the email address you've used to fill the form to buy the software. If it's not in the Inbox, then look in the Spam folder. The email with registration details was most likely caught by spam filters.
Additionally, you could contact the developers using the following email address: