SharePoint Online Unlocking a Site set to No Access

Hey,

Investigating how we could archive site collections in place on SharePoint Online, I used the PnP PowerShell cmdlet:

Set-PnPTenantSite -Url <site coll url> -LockState NoAcces -Wait

This locked the site, and removed access to it (which is a little more then what I wanted). My big concern now is that I cannot unlock it as my admin account and our SharePoint service account no longer have access to the site! 

Running the cmdlet

Set-PnPTenantSite -Url <site coll url> -LockState Unlock -Wait

under the same admin account that locked it gives me 'access forbidden' - as does our "service" admin account (which should be the primary administrator on the site).

The site collection is presented in the SharePoint admin center (with a padlock icon), but I am unable to select it.

Am I missing something? Do I need to use a tenancy global admin account?

Thanks!