iTunes not letting me play my paid-for, downloaded music.

I've been dl music from iTunes for decades. Today, from iTunes on my computer, I was playing an album of Christmas music, an album I've played every Christmas for 19 years. Suddenly the music stopped. I checked iTunes -- there was a window telling me "This computer is not authorized to play Adeste Fidelis. Would you like to authorize it?" To authorize it, I had to use the Apple Account email address for an account I had 20+ years ago -- the ISP was Adelphia, which has been defunct since 2006. Obviously, I can't enter a username and password -- if I use the old account info, I get "This Apple account is not valid or not supported." If I enter my current and correct info, I'm just reauthorizing my computer, but clicking on the album again gets me the old defunct account.

Since that ISP went defunct, I have had 3 other ISPs and 4 Macs, and each time I changed my account info and moved my music -- the music transferred seamlessly every time, no issues. Until today. I still have the old computers, and I can still play the music on them! (But they're way outdated, like High Sierra outdated.)

An hour and a half with Apple tech support didn't help at all, though they tried everything. Because I bought the music under a different account name, I could no longer play it under my current account, despite the fact I'd been playing it for 19 years under different account names but always my accounts. And again, I can't play it through the old account because that account doesn't exist anymore, but that's the only option I'm given.

And so they told me I'd have to buy the album again. Well, I bought a lot of music under that old account, and I'm wondering when this prohibition is going to show up in all that music. This seems ridiculous to me, and it has to be glitch. If I could play it for all these years, why all of a sudden am I being told I can't play it anymore -- in the middle of actually playing it, no less? It shows up in my iTunes -- it's downloaded, looks like all my other music. I can't even search for it in iTunes to download because iTunes instantly reverts to my library -- because I already have the music! I'd have to delete the music first, and no way should I have to do that.

The Apple tech (a very smart, helpful guy) was stumped and agreed it's bizarre, and said he'd escalate it to engineers, but wasn't hopeful about it. So not only am I being stopped from playing an album I paid for, but it could happen to all the other music (hundreds of albums) I bought with that account name. And despite the change in account name, it's always been me, with the same name, just changing email addresses as I moved from state to state to state. I've seen a similar problem once or twice here, but no solution that pertained to my situation, so I'm hoping that somebody out there knows what to do. Thanks.