Informed of "please contact itunes support to complete this transaction"

Then that is what you need to do.

World-wide Apple Support -

https://support.apple.com/en-us/HT204169

Support by phone, email or chat -

https://getsupport.apple.com/

Apple Support by Twitter -

https://twitter.com/AppleSupport

iTunes Support -

https://support.apple.com/en-euro/itunes-contact

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6;  HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2

See 'Your account has been disabled in the App Store and iTunes' https://support.apple.com/en-us/HT208856. This link says: "There might be a problem with the payment method that you have on file. When you see the message, don't try to edit any of your account information. Instead, contact Apple Support for help.”

Use the Apple recommended support link above first. Sometime this site is down. Use the support options I give below if necessary.

You can also Get a call from Apple support to help solve your problem https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

And you can use Apple Support Twitter https://twitter.com/AppleSupport

And, if necessary, go here to contact iTunes worldwide support via text or chat https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading, Tell us how we can help.