When did you supply it to Ebay?
They have only recently started asking for NI numbers - it is not information they would have requested when you set up your account.
Are you certain they have your NI number? What has prompted your question?
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
