@kwb737,
Some Internet accounts don't provide an option to "close". You just log out, and stop visiting to see if your account is still "open". Visiting and checking for responses and messages keeps the account active -- and tells you that you are still interested. So, just log out and stop visiting. Resist the temptation to see if you have a response or message, etc. You can also delete the URL from your Bookmarks.
If you get spam e-mail from any such account in which you are no longer interested, just mark it as junk in your mailing program, and let it slide by.