Please I want to add another payment method and cancel the old one but seems it’s not working, why?

Did you follow the steps mentioned in this article to add the new payment information?

If you need to change or update your Apple ID payment method - Apple Support

Remember that you can only remove the old payment info, after you added the new one first. Especially if you have ongoing subscriptions.

Or you can also set up/use Apple Pay (Wallet)

Direct link below:

Set up Apple Pay in Wallet on iPhone - Apple Support (HK)

This is very convenient to use and directly associated to buying anything from AppStore, iTunes Store, Apple Store and so on.

If you have "pending" payments on the existing card, I suggest that you contact iTunes Store Support Team directly and explain your problem, 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