Email notification is triggering mail from a deleted site.

Question

An approval workflow has been created for a list in SharePoint 2010, it add the 5 days to Today that was the due date for trigger mail, the site has been deleted from its environment but still the mail triggering, I just wonder there is no associated list or site for that workflow, but still getting overdue email notification. I saw in workflow there is section called "When a task expires" it trigger the mail.

Is there any way to stop email notification, what was the reason behind for that notification?