My purchase could not be completed

Then you need to do what your phone suggested and contact iTunes support at the URL provided in the message on your screen.

That is not here. This is a user to user forum and Apple isn't here. Just other users.

Hello ~You need to go ahead and contact iTunes for assistance from your iPhone message or:

iTunes - Official Apple Support

~Katana-San~

As I suggested above, the message on your screen tells you to go to www.apple.com/support/itunes/ww. and ask iTunes support. We are NOT iTunes support and we cannot help you.