Is it usual to unsubscribe from emails from a company, only to get emails from them again years later?

Yes.

Sometimes "unsubscribing" actually leads to More, since you have proven that You Exist.

Better just to teach your email service that you don't want the emial by Blocking or Trashing without opening.

Not unusual at all. Companies purchase email addresses that have shown an interest in their product or service. They may have just received your address again.