Hi Pat,
I believe I've had this happen before - and from memory the number was stuck as a 'Duplicate Value' on someone else's user profile (can't remember if they were also Inactive or Deleted).
Maybe try from within the Users Profile, add that DID as their Primary Voice in their contact information and hit save. If it comes up at 'Duplicate Value' or won't let you save, I'm pretty sure it'll be allocated to another user that's likely Inactive or Deleted and it's stuck - not sure if you keep a separate record of which user may have been assigned that number previously, or whether they'll show up in a global search.
If it does let you add the number and saves successfully against the user profile - after reloading try removing it from the user profile and save again. If it's gone from the user profile, then check if it's gone from the DID assignments page.
Hope that helps - I certainly find this aspect of Genesys Cloud (DID's and user profiles) absolutely frustrating.
As an admin, I effectively don't have full control over allocation of numbers to users and that they are so intertwined with the User Profile. This is especially true when we can't lock down users from editing their User Profile - so when a user unwittingly updates their contact information (thinking it's just a contact record) - it can and has ruined the allocation of a DID or change the behaviour of calls that is completely unexpected.
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Jeff
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