Cannot authorize new Mac to play purchased songs

I have used an external HD to transfer my iTunes library from my dying 2006 MacBook Pro to my 2009 Mac mini. Unfortunately, it will not play some of my older purchases, which were made with my first iTunes account from 10 years ago.

I long ago forgot the password for that account (I set up a new account that I've been using since), and I also no longer have access to the yahoo.co.uk email account it was linked to. I guess the MBP has remained authorized from back in 2006, but the mini is only authorized for the newer account.

I get the dialog box asking me to authorize the computer to play purchases made with Apple ID "XXXXX". When I click on the "Forgot?" link and it tries to look up that specific Apple ID, it tells me that it has no record of it.

I guess I have to get on the phone with Apple Support?