have they got support?
I had a similar issue with EA and the only way to get access was to speak to them
are you sure you know the password by the way?;
Bizarrely I downloaded the gmail app and it let me sign into my secondary account without any verification code, once I was in I could then log into my yahoo account which then sent a code to the gmail account enabling me to open up. Yahoo charge a premium rate to call them and you have to sign up for a month £5 before they will assist.