iCloud payment

If you are not going to get a replacement card, you could buy iTunes Store (not Apple Store) gift cards to the reired value and redeem then in iTunes>Account.

If you have a replacement card and it's not accepting it: it must be registered in the same country you are in and be used in the iTunes Store for that country. If that is the case, contact Support:

iTunes Store - Contact Us - Apple Support

I should get a gift card anyway to make sure the subscription doesn't expire while you are dealing with this.

I think there may be a problem going on as several people have complained that they can't change their payment method. Contacting Support is really the only option.