I need help to remove a payment method

See the Apple Support article(s) below. Link to contact Apple Support is at the end of the article.

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

See -> Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

-> set the payment methode you want to use as default payment method.