Problem with buying a certain song.

I want to buy a certain song, but it says that I have insufficient remaining store credit and it is telling me to sign in. The song that I want to buy costs $0.99 cents and I really want to buy that song. I sign in with my Apple ID password, even though I already signed in. I removed some songs off of my iPod Touch yesterday, and I want to get store credit for that. Instead, I get another screen that says Account Settings. Apple is telling me to choose a Payment Type which is a credit card. I do not have a credit card, so I cannot pay money and I do not want to get charged because I don't have one. I chose None, and it is still not letting me pay for that song. I think that everybody should get store credit if they remove songs.