That is really strange, are your emails marked operational in the settings? That is the only way people should still be getting emails if they have unsubscribed..
If there is something wonky going on you could continue to use the add choice, Unsubscribe = True, send email (empty)
Or you could create a trigger campaign that is Unsubscribes From Email = ANY
and Member of Campaign. X Name
Flow, remove from flow (your original smart campaign)
Let me know if that helps!
Thanks,
-Ryan