Hi,
Please create a new billing support request in the Azure portal. You can use below link to start the process:
https://portal.azure.com/#view/Microsoft_Azure_GTM/ModernBillingMenuBlade/~/supportrequest
If for some reason above link doesn't take you to New support request, please navigate to Cost Management and Billing, scroll down left side and open New support request blade.
Issue type: Billing, select your subscription, enter Summary, Problem type: Refund request, click Next, follow instructions. If for some reason you are unable to submit your refund request add a comment below.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP