Thank you for using Apple Support Communities. It's my understanding that your payment method is being declined. I can see how this could be concerning since you've used this same payment method for some time and there are funds available. I'm happy to help.
Please take a look at the steps and information in the link below:
If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store
Let us know if the issue persists. Please include specific error messages and any other troubleshooting steps you may have tried.
Have a great day!