Don't worry, there's probably a simple solution.
We take payment for an order when it's delivered, not when you complete your payment at the checkout. So, if your card is due to expire before we plan to take a payment, it may not be accepted. Unfortunately, we can't verify your new card either, as it can't be activated until your current card expires.
If you think it may be something else, you'll need to contact your bank to make sure there are no other problems with your card. They will undertake the verification process on our behalf.