AT&T owes me $500 deposit for almost one year!!! How can I get my money back?

Hi there,

Here I beg for anyone's help! I have really been outraged at this point.

As I am an international student, I joined the "Family Plan" with my friends (they are all international students) since 10/11/2012. All of us (5 people) signed the two-year contract for iPhone 5 and each person was charged for $500 as security deposit since none of us had a SSN.

However, in November 2013, AT&T sent us the check only with the amout of $2,000 (it was supposed to be $2500=$500*4); as a result , $500 was gone for no reason!!! (We paid our bills on time every month) I visited many stores but no one could helped! I also made countless calls and still got no solutions. What ridiculous is, the representatives claimed that we only paid 4 deposits at the begining.

Actually, we do have the receipts of the deposits. While things went weird, by coincidence, one of our members lost his receipt. That is, we currently have only 4 receipt in hand. Now it almost been one year while ATT still owes us $500. I feel really helpless, hopeless and even speechless.

Is the wolrd seemed to be controlled by  oligopolies, normal people have no choices but being coerced among them. Whatsoever, I have to get my money back! If anyone has the experience like me? I need your helps! Thnak you very very much!!!