Hi,
Windows licenses are not refundable, but since you purchased it accidentally, I suggest reaching out to Microsoft Billing Support directly. There might be an exception in your case.
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.