What do you mean by 'refusing from the system', if you are getting an error message then what does it say ?
For a credit card to have a chance of being accepted it needs to be registered to the same name and address (including format and spacing etc) that you have on your iTunes account, and have been issued by a bank in the country where you and your iTunes account are. If it is and if you are getting a 'declined' message then you could check with the card issuer to see if it's them that are declining it, and if not then try contacting iTunes Support (these are user-to-user forums) and see if they know why it's being declined : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption
If when trying to download you are getting a message about a 'problem with a previous purchase' then that implies that iTunes wasn't able to collect the money for your last purchase. If that is the case then you won't be able to download anything else (including app updates) until you've paid off what you owe : Pay an unpaid balance in the iTunes Store - Apple Support
If you aren't getting the 'problem with a previous purchase' message then try logging into your account (not when trying to download something) and see if you get the 'none' option so that you can remove the card's details and be able to download updates to your apps : Change or remove your payment information from your iTunes Store account (Apple ID) - Apple Support