How to get iTunes to accept my new VISA credit card?

I know this topic keeps coming up but I can't find any site which tells me how to add a new credit/debit VISA card to my existing iTunes account. My old one was working fine until I lost it and replaced it with this new one and I DO have a subscription tied to this new card but I can't get iTunes to accept the card. Keeps telling me the info is incorrect. Help! How can I fix this?