Why when I key in my payment information ,always show MSG : for any assistance pls contact I tune support?

If you are getting a message to contact iTunes Support then you can do so via this link and ask them for help (we are fellow users on here, we won't know why you are getting the message) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption