Thanks for the response. I've attempted the post-migration process but unfortunately I don't have access to the account email any more. I can login and start the process, however, I can't get the email code it sends out (which is why I couldn't migrate in the first place).

If you do not have access to the email your Mojang account was associated with, we will not be able to update the email to a new one for you to be able to claim the code. If you do not have the email, you may reach out to your email provider for assistance. -JL