Outlook group contact reappearing after removal

One of my users has an Outlook group with 15-20 contacts in it. A terminated user's email address refuses to be removed causing email bounce backs. When removed from the group and refreshed the contact reappears after changes were saved. Keep in mind that other contacts have been added and removed without issue. I have attempted to remove the user via desktop app and OWA. Cleared web cache, cookies, etc. Account has also been fully deleted from 365 at this point yet the contact remains. How do I banish this contact?