Hi,
You can create new billing support request using Azure portal, that way you can discuss getting refund with billing support person. From your description you were close to getting the case opened, but there is a small detail to get out of endless loop.
It is critical to follow the steps below carefully.
1. Navigate to this link to start the process:
https://portal.azure.com/#view/Microsoft_Azure_Support/HelpAndSupportBlade/~/overview
2. Click Create a support request button at top
3. Click Switch to old experience button on right
4. On left, enter billing in the box and click Go
5. Select Billing and click Next
6. Select your subscription from the dropdown and click Next
7. At this point there will be a delay of several seconds, and then various options will be displayed. Click Create a support request button at the top. Do not click any of the other options.
8. Fill out screen, Summary, Problem type, Problem subtype, then click Next button at bottom
9. There will be another several second delay, and then some solutions will be displayed (this is similar to above). DO NOT CLICK any of the solutions, instead click on Return to support request button in upper left corner, similar to below
10. Now you are back at support case. Click Next button at bottom to continue to Additional details tab. Fill out information as required, one of the items you need is your Subscription ID.
You can open separate browser tab and navigate to your subscription in portal, the ID is there, click the copy button to the right of it, then paste it into the box on Additional details tab. Click Next to advance to Review + create tab, then click Create.
You should receive an automated email within a few minutes and then be contacted by support within 1 business day.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP