Unsubscribe rate is resetting itself every month

I was sent a campaign in Feb. And approx 45 subscribers was unsubscribe from mail list. When I check same campaing report today, 4th of March, only one subscriber shown in unsubscriber list.

How can I see whole unsubscriber list for old campaign?

Thanks in advance,

If you take a look at /backend/index.php/settings/cron in the "Subscribers settings" tab (last one in page) you will see some settings for how much to keep subscribers in the system when they are under certain state. You will see that, by default, "Unsubscribe days" is set to 7, which means any subscriber that unsubscribes, is removed from the system after 7 days. You can increase this value to keep the subscriber longer.