I would suggest trying to call at&t - read the very end of my 1st post and you'll see what I had to do because it didn't initially work for me either.
Can I have an online rep change it for me? Like when I log into OLAM and have the chat box come up.
One thing that I see that can be an issue is when you log into OLAM and under data usage history it has all the data plans listed under there that I had previously had under this billing cycle, which was the 2GB iPhone data plan, wouldn't that be a red flag to the person that I ask for unlimited data plan for the iPhone?