How to resolve 'Cannot Add Payment Method' and 'Billing Problem' on Apple Account?

Now I cannot Add Payment Method. Also cannot Remove old payment methods. I cancelled all my subscriptions, sign out and signed in, tried on different iphone. But still got these problem. please help.

[Re-Titled by Moderator]

Original Title: Last time I couldn't pay icloud+ subsription after that time my account have Billing Problem, The iTunes Store cannot process purchase right now errors. How can resolve these problems.