We have had couple of clients complain that we keep emailing them despite them repeatedly asking us to change the primary email for estimates and recurring invoices.
Today i have identified the issue it is gocardless.
Can you retrieve the default Go-cardless contact and display it on the customer page
Later on you could possibly prompt if the primary account was changed and the same email address on gocardless to but that is not as important as visibility.
Thanks Loving your work