Cannot change Adobe ID email — confirmation code is sent to my old email address, which I can no longer access

My Adobe ID's primary email address is an old Japanese carrier address (…@docomo.ne.jp) that I can no longer use or receive mail at, because I changed carriers. I can still sign in to my account with that ID and password.

When I try to change the primary email to my new address, Adobe requires a confirmation code sent to the OLD email address ("verify your old primary email address"). Since that mailbox no longer exists for me, I cannot receive the code, and the change cannot be completed.

I contacted Adobe support chat. The agent suggested abandoning this account and creating a new one with the new email address. However, this account holds my Illustrator CS6 perpetual license registration (registered in 2013), and I am worried about losing that registration. I asked whether support could change the email on their side, or verify my identity in another way (I have identity documents and the original purchase receipt for the CS6 license), but the chat was closed without an answer.

Question: Is there any official way to change the primary email address when the old address cannot receive the confirmation code? If Adobe staff can review my case, I am happy to provide proof of identity privately. Thank you.