Unsubscribed a contact but they still received an email

Has anyone had an issue with Unsubscribing contacts? This particular person did not click the link in the email, rather he replied so I did the unsub for him and then logged in and searched his name to confirm it worked which it had.

Today he sent an email saying he had received another email and understandably is rather unhappy. Has anyone had any problem unsubscribing contacts and it not working? Or does anyone have any tips to ensure they are unsubscribed?

Thanks

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