Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi PPG,
From my side, I added a mailbox as delegation under my mailbox, then I go to Office 365 Admin center to remove it, everything is fine from my side. To better help you, we suggest you run the PowerShell command to remove it again: Connect to Exchange Online PowerShell and Remove-MailboxPermission. After that, you can go to Office 365 admin center > active users > choose this user > Mail Settings to see if the delegation was removed.
Meanwhile, we also have a little unclear on "I got back in to check, the previous permissions are still there" and " delegations I want to remove are not listed". May I know if you mean you still can see the deletetion under your mailbox, but the deletation donesn't under the Outlook's list?
We also welcome to you remove the delegation again from the admin center like below:
Note: Please check if the delegation is under the "Removing".
Thanks,
Richard