Is it possible to change the email address with which I access my Zoho Billing account?
Yes, you can change the email address with which you use Zoho Billing by inviting yourself as an Admin user to your organization with the new email address.
If you are unable to add more users to your organization or want to change the email address of your Zoho account itself, you can do so by visting this page. On this page, go to the Email Address tab under Profile, where you’ll be able to add a secondary email address and mark it as primary.