Cannot remove visa

See -> Add a payment method to your Apple ID

Add a payment method to your Apple ID – Apple Support (UK)

• If you want to change your card, add first the new card, then remove the old one.

Perhaps you have pending payments on that card. In such a situation, I suggest that you contact iTunes Store Support Team directly, using this specific link:--> Apple Support

(if you get no help, look at the bottom of the above link, where you can contact them using "chat" or "phone" options).

Regards

Giulio