If you used the process on this link to cancel that subscription, then if applicable, you should automatically get a pro-rata refund:
They provide more information on refunds on this link:
If you are still unable to resolve the problem, this forum is just a user to user forum, no-one here has any account access, it would be best to contact their support, try using this method to contact their support.
Go to this link: https://support.microsoft.com/contactus
Select Microsoft 365
Click 'Get Home Support'.
In the box provided, type billing.
Press Enter, then on the next page, scroll down and click 'Sign in to Contact Support'.
Navigate to Microsoft 365 and Office - Manage my Subscription.
Select the 'Chat with support agent in web browser' option