Hey @Madhu Soodhanan! Daniel from Customer Support Engineering here  

We don’t have a way to check the timestamp of historical unsubscriptions at the moment. You can get alerted when a user unsubscribes with our contact.unsubscribed webhook model. However, this won’t give you insight as to what campaign caused the unsubscription; you may find an analytics tool such as Google Analytics to be more useful for this functionality.