Can my locked AT&T Note 2 be used on Straight Talk?

I recently purchased a used AT&T Samsung Galaxy Note 2 from a company who sells used/refurbished phones named Digicircle. The phone is in mint condition and has a clean ESN/IMEI however it is locked to AT&T. I'm a customer of Straight Talk (ST) and my AT&T compatible ST sim card is not working in the AT&T phone. However, I thought it would automatically work when I inserted the sim card but instead a "no service" sign shows up at the top and sometimes the service will come in but majority of the time it has the "no service" sign. So I assumed that the phone had an antenna problem as the sim works when I plug it into my AT&T iPhone 4. I called ST and they told me that the phone must be unlocked. The only problem is that AT&T won't do it unless I have the information of the individual who had the phone with AT&T to unlock it. But there's no way I could get a hold of that info out as the individual sold it to the company and the company sold it to me. Can ANYONE help me? I know unlocking phones are illegal now… What should I do? I need help As soon as possible

Did you change the APN settings on your phone? There are instructions on how to do this on the Straight Talk website. Try that before you try to get your money back or unlock your phone.