I need help! What do I do!?

If it's a debit card that might be why, not all seem to still work with iTunes. You could try just logging into the account (not when trying to download anything) and see if you can remove the card (and possibly then also try entering its details from scratch and see if it then works) : Change or remove your Apple ID payment information in the iTunes Store - Apple Support

For a 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 are (and therefore the country which is on your iTunes account).

Apple ID payment information - If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store

If necessary, contact iTunes Support. Scroll to the bottom of the page in the 2nd link.

iTunes Support

iTunes Support – world wide