First, I tried to make 2 new accounts at the page
http://www.spamcop.net/ces/account_new.shtml
then successed and the Billing Information page was
shown.
Then, I remembered that I need one more account and
returned to the page before billing.
Next, I entered the 2 accounts again and added one new account.
But, following message was shown...
"Sorry, this email address is already taken. Please change it and try again."
Is it possible to remove the non-billed account and use it again?