Before requesting a refund make sure you have unsubscribed from Pro, more information is available here.
All of our in-app purchases and subscriptions are billed by Apple’s In-App purchases. This is for your security and privacy, we do not have access to your banking/credit card information and will never ask you for your credit card number or other personal information.
Developers can not directly issue refunds for App Store purchases, in-app purchases or subscriptions, however refunds can easily be requested from Apple.
The link below has helpful instructions on how to get refunded.
Request a refund for apps or content that you bought from Apple