Mistakenly Purchased the Upgrade Version

I mistakenly purchased Parallels upgrade version instead of the full version. How do I correct my purchase without incurring a charge for both the upgrade and new version? Thanks.

 

Hi the best way to resolve this issue is the fully refund your previous purchase and then you will be able to purchase the full license.
Please confirm the refund and provide us with your order number.

 

Thanks. How do I complete a full refund of my prior purchase.

 

You may provide us with the purchase order number and then we will refund your order and send you an official email with additional information.

 

by mistake I purchased an Upgrade to Parallels Desktop 18 instead of a full license, how can I solve this problem because it indicates that I must put the previous product key