See -> Remove a payment method from your Apple ID
Remove a payment method from your Apple ID - Apple Support
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If you can't remove a payment method
👉 If you have subscriptions like iCloud+, have an unpaid balance, or you use purchase sharing, you must keep at least one payment method on file.
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You can have a credit card / debit card on file and an Apple Account balance.
Your default payment method will be used first by Apple when you need to make a payment.
If you have set your Apple Account balance as your default payment method and you have a CC / debit card, you pay from your default payment method.
If your Apple Account balance is 'empty', Apple will charge your credit card / debit card on file.
See the following Apple articles:
Add money to your Apple Account balance
Add money to your Apple Account balance - Apple Support
Add a payment method to your Apple ID
Add a payment method to your Apple ID - Apple Support
Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
If you still need help, get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service or check -> here for more support and assistance.