I've had that experience tons of times, where companies are happy to unsubscribe me if I just give them the account number that I don't have because I'm not their customer.
On the other hand, I was getting Allstate billing notices for someone else and I was surprised how well they handled it. When I called, they understood that I was a third party and apologized. They were able to look at a record of all the email sent and verify I had not received any sensitive information (only last 4 digits of account number, first name, and bill total). They removed my email address and said they would contact their customer immediately.
The only way they could have handled it better would have been following best practices and sending a verification link as their first email. :)
On the other hand, I was getting Allstate billing notices for someone else and I was surprised how well they handled it. When I called, they understood that I was a third party and apologized. They were able to look at a record of all the email sent and verify I had not received any sensitive information (only last 4 digits of account number, first name, and bill total). They removed my email address and said they would contact their customer immediately.
The only way they could have handled it better would have been following best practices and sending a verification link as their first email. :)