Remove credit card

Hi

i have had this problem myself,

this link is useful and shows how to do this> Change or remove your payment information from your iTunes Store account (Apple ID) - Apple Support

if you have a pc with iTunes , you can change your payment type by going to iTunes store > account tab> payment info > select none

the reason the iTunes store request a c.card is for verification purposes > below link explains this

About payment card authorization holds in the iTunes Store - Apple Support

You are just logging into your account, you're not trying to do it when trying to download something ? If you don't get the 'none' option on the payment details screen : Why can’t I select None when I edit my Apple ID payment information? - Apple Support

And what do you mean by 'my App Store doesn't work' ?