If you're answering the default question correctly and it's not being recognized, you may have forgotten some minor details of your original answer to the question, like the word "the" or "a" or a comma. You will have to contact technical support at the site that hosts your e-mail to have the account reset. That's unfortunate, but it happens. They should have no difficulty helping you. They may insist on transmitting a code to your cellphone to verify your identity.