Remove Credit card information

Changing/removing payment info : Change, add, or remove Apple ID payment methods - Apple Support 

If you don't get the 'none' option on the payment details screen : If you can't remove your last payment method or use no payment method with your Apple ID - Apple Support

Apple ID without a credit card  

Apple ID payment information - If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store

Why they just says it failed and decline on my credit card information

I need to fit my iTunes I can’t purchase on my phone

Can you help please

What is 'I need to fit my iTunes' supposed to mean ?