Thanks for reaching out to the Apple Support Communities. I understand you've had some trouble changing your payment method, and I have some information that may help.
If you've had a previous issue with the payment method, you may need to switch to a new method to bring your account current. Afterward, you can still change back to your preferred method. Have a look at the article below for some helpful troubleshooting steps. If the behavior persists or you run into any trouble, please reach out again.