Hi @Anonymous Thanks for posting your query on Microsoft Q&A.
I would recommend following the step by step guide using Azure PowerShell (if not checked already) , as per your requirement, , to
Delete an Azure Backup Recovery Services vault
or
Delete a Site Recovery Services vault
If you are looking for deleting Azure Backup Recovery Services vault, please check the following pre-requisites :

If you meet all the pre-requisites, then the next steps involve using Remove-AzRecoveryServicesVault command after Disable-AzRecoveryServicesBackupProtection command.
If you have already tried these steps in the document and still stuck, please let me know in the comments and I can further investigate.