How to change the Billing contact's email address
Summary
New invoices will be send as PDF to the email address set in the Billing Contact. This article describes how to change this.
Start
Go to the customer
Click 'Account' (Suitcase button)
Click 'Account Profile'
Click ‘Edit' and edit the Billing contact’s email address

To prevent the invoice from being created and sent entirely follow How to disable or enable customer invoice notifications