Have you considered events from their perspective? From what you've described, they were told to wait until a notification was sent, then they were given a notification with the instruction "send this". If it was me my first thought would absolutely be that that's the notification to be sent, the only reason I'd hesitate is because those sort of communications are well outside my job description.
The reason they sent the product afterwards is obvious; they were told to send them after the notification was sent, and they had sent the notification.
From what you've described, you are communicating incredibly poorly then blaming your workers for misunderstanding.