iCloud sign in confusing my current email with my old email

When I first created my apple id, my email address was petermbooth***@gma**.com. After a few years, I changed my email address to peterbooth***@gma**.com

For several years I have had Messsages set up on both my iPhone and my Macbook Pro. Today, I was having a problem with Messages on my Macbook (which I won't get into here) and in an attempt to resolve it, I signed out of Messages. Then I went to sign back in. No problem. I put in my current email address and my current password and all was good.

Then I tried to send a message and up popped a dialogue box asking for the password for my OLD apple ID. I don't know that password and I can't get past the pop up.

When I exit from the pop up and go to Preferences within Messages, I can see that I am signed in with my current apple id.

This is frustrating and I'm wondering (a) how I can get past this so I can use Messages from my Macbook they way I have for years and (b) how I can tell apple that my old email address is no longer "a thing" and delete it from everywhere in the world. 😊

I'm using a Macbook Pro from mid-2014 with Big Sur 11.7.10

Thanks for any ideas on how to resolve this.