Hi Barry Walker,
Welcome to our forum!
How did you delete the duplicate Contacts? Could you please describe the detailed operation?
As I know: Deleting a contact in Outlook on the web removes it from all Outlook clients. However, if that contact was hidden in Outlook on the web, the contact card reappears until all hidden duplicates are removed. Please refer to the article Manage duplicate contacts in Outlook - Microsoft Support and try again.
In addition, you can also try to merge duplicate contacts using profile cards in Outlook on the web. More information: Merge duplicate contacts in Outlook - Microsoft Support
Hope it helps.
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