Another option is to contact mojang support. They ask for the following information to change the email:
Account Username:
Email Used to Create Account:
Do you have access to this email:
Any other emails you may have had on this account:
City and Country of Account Registration:
Transaction ID from Purchase:
Month and Year of Account Registration:
Date of birth:
If you can provide accurate enough data for the account they will change the email to a email of your choice. In this way you can keep your original account and still migrate. If you no longer have access to the TID (Transaction ID) you can say that its either lost or you can look in your bank records and find the TID there. Mojang has written a whole article on it that you can find
here.
If you decide you want to go this route you can make a mojang ticket
here. Do keep in mind that because of migration mojang support is slow and thus this can take some time.
Goodluck on migrating or getting your rank transfered :)