Hi,
Digital purchases such as a Windows 11 Pro upgrade are generally non refundable. However, if the purchase was made by mistake or accidentally, I recommend contacting Microsoft Support as soon as possible. They may be able to review your case and make an exception depending on the circumstances.
Click this link: https://support.microsoft.com/contactus/
Sign in to your Microsoft account.
Select Windows > Click 'Get home support'.
Type "Chat with an agent" from the text field and press Enter.
Click "Contact support" at the bottom.
Select the product you need help with.
Follow the prompts to connect with a live agent or request a call back.