Earthlink has bought so many ISPs now, that's not surprising! If it's an Earthlink company, your CC company can contact Earthlink and request his info. They won't give it to you as an individual -- fortunately they don't give out addresses and such to just anyone who asks!

If your CC won't follow up (they may consider it too small for the time it would take), you could forward the information to abuse@domain.net and report him. If nothing else, you might get 'em to cancel his email account :)