Majority of Contacts Have Been Marked as "Unsubscribed"

Majority of Contacts Have Been Marked as "Unsubscribed"

I recently noticed that all but 6 of our master list has been marked as "unsubscribed" (approx. 6200) with the exact same time stamp.  This is a critical issue because we can not send out any future campaigns to the majority of the contact list.  It doesn't seem to make sense, because the dashboard of the last campaign does not indicate that level of "unsubscribers" and it is not practical to have over 6000 contacts unsubscribe at the exact same time.

Could you please advise on what possibly happened and how to remedy the problem?

We currently pay for the service.

Thank you.

Anne