How to remove your Hubpages account
From their FAQ:
If you would like to close your HubPages account, please sign in to the account that you would like to close, unpublish all of your Hubs, and send an email request via http://hubpages.com/email/help/close with the subject “close my account” and the username of the account you would like to close in the body of your message.
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for Hubpages using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Hubpages. Click here to find out how.