No one can help you. AT&T will only unlock phones for current or former customers that had the phone on their account. You will need to go back to the person that sold you the phone to get it unlocked. No one here can do anything to unlock your phone.
This is a user to user forum. I am a user, just like almost everyone else on the site.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.