Problem with alternate mail

hello,
i can't access my account. and i have 2 solutions: answer the security question (that i can't remember!) or ask a code from yahoo that need my alternate mail.
the problem is that i have not remembered to create that alternate mail. so i don't know the password! and when i want to open that alternate mail, yahoo says "This ID is not yet taken"!
now, how can i access my account?
and is it possible that this problem related to the spam that was recently sent from my account to my contacts with my signature and name?
it's too necessary to access my account.
tnx.