@Semen Anikin - I have checked the details of the case and it seems you have removed and deleted the data source from backup on 09-Nov and this data is currently in soft delete state for 14 days. Once 14 days is completed which is on 24-Nov then you would be able to remove the MARS registration from vault and then delete the vault.
I wish there was a way for you to remove AlwaysOn Soft Delete but currently it is not available.
Just to update you that Microsoft does not charge you for 14 days retention of data in soft delete state. But if you immediately want to delete the vault and does not want to wait for Soft delete period then you can reply on the case and the backend team will help on unblocking it from the backend.
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