Payment information

Apple ID without a credit card https://support.apple.com/en-us/HT204034

Apple ID - If you can‘t choose None when you edit your Apple ID payment information. https://support.apple.com/en-us/HT203905

Buy/redeem iTunes Gift cards to the account.

App Store & iTunes Gift Cards by Email. https://www.apple.com/shop/gift-cards/itunes-electronic?product=D7456LL/A

Gift cards redeem. https://support.apple.com/en-us/HT201209

Gift Card - can’t redeem. https://support.apple.com/en-us/HT201195

If necessary, contact iTunes Support. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.

iTunes Store - Contact Us - Official Apple Support. https://support.apple.com/en-euro/itunes-contact

iTunes Support – world wide https://support.apple.com/choose-country-region/itunes

In the meantime you could use iTunes Gift Cards as a payment and if necessary, set the payment info to "none".

Change, add, or remove Apple ID payment methods - Apple Support

If you can't remove your last payment method or use no payment method with your Apple ID - Apple Support