MacBook Air asking for old Apple ID password when logging into FaceTime and iMessage

I recently purchased a MacBook Air 2020. I used Migration Assistant to transfer my data/settings from my MacBook Air 2013 to the new one.

I logged in using my current Apple ID and everything was working perfectly, except for FaceTime and iMessage. iMessage returns a message of 'unknown error occurred' and won't let me log in and access messages. On FaceTime, I enter the username and password of my current Apple ID, it waits a few seconds and then prompts me to enter the password for the old email address that I used to use as my Apple ID years ago. It is not an old Apple ID account, rather I changed the email address of the account to a new email some years ago. Therefore I can't reset a password or find other ways to access the 'old' account, as it is technically the same account.

Steps I have taken so far:

Logged out and back in to imessage and facetime on my iPhone, ensuring the correct email for the Apple ID was showing

Restarted the MacBook (several times)

Logged into my Apple ID on the Apple website to ensure there is no trace of the old email address

Logged out of iCloud entirely on my MacBook and signed back in. This seems to have exacerbated the problem and now I get a prompt to enter the password for the old email address in my system settings for Apple ID and iCloud.

Please can anyone suggest any fixes? I essentially have a MacBook at half functionality at the moment because of this issue. Thanks in advance.