I want to update my payment information, it is not working, please assist me

If you already followed (to no avail) all the steps provided in this support article:--> Change, add, or remove Apple ID payment methods - Apple Support (assuming you have no pending payments on the card(s) you currently use), I suggest that you contact iTunes Store Support Team directly, using this link:--> iTunesStore & App Store – Get support for various issues, choosing: your country, then Apple ID, then iTunes & App Store. If your problem is not among the options shown there, tap/click on the option “the topic is not listed” and describe your issue.

Regards

Giulio