Hello
What is the name of the app? Certain apps requires a different install if you upgraded/paid for it in-app, so you might run into that issue. One typical example is the Movie Maker vs. Movie Make pro, you will need to install the Movie Maker Pro as a separate app. Not sure if that's the case.
Otherwise, refund needs to go through billing support, not here in the community forum.
To get help, open the "Get Help" app on your computer (just search for it in the Start menu). or go to https://support.microsoft.com/contactus, Type "Billing" and press Enter. On the next screen, click "Contact support" at the bottom of the page, then choose "Windows" > "Manage my subscription". You’ll then see the option to chat with a Microsoft support agent who has access to your account to help review the issue.