Check your spam folder. Unless you did not complete the transaction, I can guarantee the an e-mail was sent. Also did you save the page on your browser when you bought.
Check browser history. An order number should show up, again if the transaction was completed.
Contact support with your email address they can look up your order.
Go to this page and enter your email. When you get the order number go back to the same page and enter email and order number to get the key.
eSellerate After-Purchase Services