Hi mattdanwade,
Welcome to the Apple Community, where some of us do our best to help each other.
Wondering where you tried to update your payment information ?
For the App Store and iTunes etc., your card may not be listed in your Apple ID account
Apple has a support articles that may be of help to you:
Change, add, or remove payment methods in Apple ID
https://support.apple.com/en-us/HT205583
Payment methods that you can use with your Apple ID:
(Scroll down to find your country)
https://support.apple.com/en-au/HT202631
This is a link to the Apple ID log-in, where you might be able to update the payment information:
Apple ID Log-in:
https://appleid.apple.com/
OR
If it is Apple Pay ?
Manage your Apple Pay account:
https://support.apple.com/en-us/HT209228
Manage the cards that you use with Apple Pay
https://support.apple.com/en-us/HT205583
Hope this helps you :)