why i can not change my payment method

See this article about updating payment methods on various platforms (iPhone, Mac, etc.): If you need to change or update your Apple ID payment method - Apple Support

"If you change your address, the credit or debit card information that you use with your Apple ID might be automatically updated by your financial institution, and you don't need to take action. But if there's an issue [such as you having a subscription or being a Family Sharing Organizer], add a new card first, then remove the old card."

It does not mention an Apple TV. You can also add a payment method after signing in to appleid.apple.com.

In some countries and regions, when you edit payment information online at appleid.apple.com, additional payment methods might be removed from your account automatically.