Use this link to check the status of Apple’s various services and servers —>
Apple - Support - System Status
If there's no problem there then it's possibly a problem in whatever routing Apple takes to communicate with your bank. It could even be your bank is down, or you card indeed has problems. Apple is simply sending out a request for card verification and either getting one saying it is no good, or it isn't getting any kind of reply.
I would contact your bank first before contacting Apple. All Apple probably knows is the non-verification status. If your bank says it is not at their end then you are playing monkey in the middle. Here's how to contact Apple: Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This page has telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support