Re-activating unsubscriber after a purchase

Hi there,
We have a number of customers that have at some point unsubscribed from newsletters/updates, which has unsubscribed them from everything.
They then purchase and don’t get their followup campaign for one of our programs (or other material they have asked for.) We don’t know this until they contact us to say they have no information sent to them.
I have setup the email confirmation at the beginning of the campaign series, but it is not triggering the email to those who have been unsubscribed.
This really concerns us when people want to opt back into information as it is not sending the necessary email to re-subscribe.
Is there any way we can send the email confirmation automatically in this situation? We know how to send the confirmation manually if a customer contacts us.

This is what is happening. I feel that this is a major problem for those who do want to receive emails again.