I need to remove my card details

See the Apple Support article(s) below.

Apple ID without a credit card      

Apple ID - If you can‘t choose None when you edit your Apple ID payment information.      

anoria Said:

"i need to remove my card details"

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At Least One Methods of Payment:

You need at least one method of payment to assign to your Apple Account. 

So, either:

I. Contact Apple Support directly:

Apple Support Contact Information:

• Contact Us - Choose Locations
• U.S.A. (800)MY-Apple
• Proceed from there as Necessary

Or...

II. Manually Manage this:

A. Go Here: Manage your Apple IS - Apple Support

1. Scroll Down: to Payment & Shipping
2. Select: [this method of payment]
3. Remove: [this Method of Payment]
4. Add: a new method of payment

Note: (it might be more user friendly if you were to use a computer rather than your iPhone to perform this).

Or...

B. Assign a PayPal Account:

If you have no other cards, then you could probably open a PayPal account (if an option to you). You would assign that as your method of payment, rather than a card. Once, added to your account, remove this card using the above link.