@Peter Kirkpatrick Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
Apologies for the delay response here!
Billing and Subscription team would be the best to provide more insight and guidance on this scenario: https://azure.microsoft.com/en-us/support/options/
Additional inforamtion : If you cancel an Azure Support plan, you're billed for the rest of the month. Cancelling a support plan doesn't result in a prorated refund. For more information, see Azure support plans.Please let us know if you have any further queries. I’m happy to assist you further.
I was still charged even though my Azure subscription was deactivated
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