Can't enabe Internet Sharing

Hello,

I am from Philippines. I got my AT&T-labeled Nokia Lumia 520 from a Bounty Program of Bug Reporting from Microsoft. The problem is I can't enable my "Internet Sharing" feature, it say I need to go to att.com/mywireless, and when I go to that page I need to be registered and I can't finished because it needs a subscription or something.

Thanks for someone who will help.