Broken (?) Extend Xbox LIVE Gold Trial for $1 and two free games: The Maw and Aqua

I tried clicking the "Gold for $1" link at:
http://www.xbox.com/en-AU/Live/GoldExtension

This offer includes a month of Xbox LIVE Gold and two games: The Maw and Aqua. But an error appears:
Uh oh… that shouldn't have happened.
It appears you've found a glitch in the system.

I've tried with a silver and an account with a gold trial (included with my Xbox console). Anyone know why? To redeem this offer Xbox support said I need a 30-day trial of gold, which is no longer available. Are they right? Is the 30-trial no longer available? Apparently the gold trial that was included with my Xbox console is a prepaid membership.