Hello Llewellyn Thomas,
Welcome to Microsoft Q&A Forum, thank you for posting your query here!
We apologize for the inconvenience. I understand your concern about being charged monthly despite having deleted the resources and canceled the subscriptions.
As you mentioned, you were unable to delete one of the final resources (a vault associated with a resource group), which is likely the reason for the ongoing charges. because these resources may still be active on the backend even after the subscription is canceled.
To stop these charges for you, you definitely need to delete the vault with its associated items first. Since you have tried and failed to do this due to the inactive subscription, you will need to re-enable the subscription to complete the deletion.
However, I understand that you are not interested in re-enabling the subscription. In this case, you will continue to be charged until the resources are properly deleted.
Since you cannot delete these resources from your end, Microsoft can assist you, but we require an active subscription to proceed with the deletion. So, please enable the subscription and delete the resources to stop the charges.
Note: If you cancel your subscription with pay-as-you-go rates accidentally, you can reactivate it in the Azure portal.
If your subscription isn't a subscription with pay-as-you-go rates, contact support within 90 days of cancellation to reactivate your subscription.
How to contact support:
Here are the steps.
https://learn.microsoft.com/en-us/azure/azure-portal/supportability/how-to-create-azure-support-request
To delete the vault and its associated items:
refer to the below doc.
https://learn.microsoft.com/en-us/azure/backup/scripts/delete-recovery-services-vault
After the resources have been deleted, you can proceed to cancel the subscription and close the account.
Below are the steps to cancel the Azure subscriptions.
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Thank you.