If you click where it says "Download Game Client" after opening the Diablo III section, it should give you the two choices for clients. Retail and the Public Test Realm. The only requirement is having a Diablo III account in good standing.

It would have to be his account then. What's his BattleTag id? Don't post his email address in here.

I'm not seeing any problems with the accounts that would explain you not being able to see the PTR client for download.

I'm afraid you'll need to submit a support ticket and see if the Billing Reps can help with this.

This article will lead you through the process.

http://us.battle.net/support/en/article/contact?utm_source=internal&utm_medium=support_forums&utm_campaign=BlizzardCS