See If your payment method is declined in the App Store or iTunes Store https://support.apple.com/en-us/HT203005. If you need additional help, use this support link from the document https://support.apple.com/contact
But, also see these reads pertaining to a related error:
Payment method declined in iTunes or the App Store ...
Fix 'Your Payment Method Was Declined' Error In App Store
Why do I keep getting a message that my Apple payment ...
Also, can get Apple telephone support for help in solving your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 Be patient sometimes Apple support is closed to immediate phone support.
or useApple Support Twitter https://twitter.com/AppleSupport. There may be a wait.
And here is how to contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading Tell us how we can help.