I hear you! I've had four different providers the past 29 years and all of those email addresses have now disappeared. My present provider doesn't even offer email which is why I'm glad I still have my Yahoo address.
You might be surprised to learn that those email boxes didn't actually disappear, unless the service provider managing them disappears. Many internet services let you take them with you. I used to have AT&T internet, (@sbcglobal) and still use that email separate from AT&T service.
The mailboxes likely stayed active after you cancelled service.