The most common reasons we see for payment failure are:
Expired payment details: If your old card has expired and you have new payment details, please ensure that you update them on the system to continue access. Some banks enable expired cards to still be processed a couple of months after they have expired, so this might be relevant even if your new card came through a couple of months back.
Select here for the guide on changing payment details.
Blocked charge: If there is not enough money in your account, then the bank will block the charge. Please ensure there are enough funds in your account when payment is due to ensure that you still have access.
If you are not sure why the payment failed, then please contact your bank. They should be able to provide more information and guide you on what needs to be done.