The Parallels Mobile app sold in the Mac App Store is software that is being sold by Apple. As such it falls under the Apple App Store Return and Refund policy:
Apple does not permit return or offer refunds for products purchased through the App Store, including Parallels Mobile. Unfortunately, we are unable to process returns or refunds for Parallels Mobile sold by Apple.
Should you have any further questions, please feel free to contact Mac App Store Customer Service directly: