Every time I try to download a free app it asks me for a credit card? Saying I have a fee?

I have an iPhone 4 and on this app I purchase and I got it and now the app store saying that I owe but i still have what I purchase, but the app store still want the card info but saying use another card since other one been decline

You haven't asked a question.

A card has to be on file in iTunes no matter the purchase. Why? Lots of apps are free but they have in-app purchases that cost money. You can remove it later. Best luck.