Accidental purchase of upgrade

I have accidentally purchased the upgrade instead of the full install. It's genuinely bizarre that the upgrade purchase doesn't ask you for the previous version key until *after* you have purchased it but, I would like a refund on the upgrade so I can purchase the full version.

 

Please take a look at the e-mail that includes your product activation key for the link where you can get your order refunded.

 

Hello, we have sent you a private message. Please help us with your payment reference number or the Parallels Desktop for Mac license so that we can initiate the refund. Thanks.