Why does it keep asking for my credit cardinformation when I try to redownload an app

They use this info to charge you for paid apps, if you already downloaded an app, they will ask again, but after that it will say that you already bought it and give you an option to download it free after you put in the information. If it doesn’t ask and you want a refund, go to Request a refund for apps or content that you bought from Apple - Apple Support.