Payment problem

Hi, I've been trying to purchase a song.

I did not have any problem with my previous purchases.

However today, as I tried to do so, it told me my billing information is incomplete, to which when click on it, and try to manage my payment, it did'nt allow me to.

it kept asking me to key in my password, but not in any way getting me to put in my card information.

Please advice.

Thank you.