Deposit Refund -Super Disappointed!

This issue has been killing me for 3 months in which I have called costumer service over 20 times! can you imagine 1 hour each call, and I still cant get my deposit back!

4 of our family plan members (including me) made $500 deposit each in 2011. AT&T returned two of them, one was in December 2012, and one in Feb 2013. But still two deposits mine and another friend's havnt returned back.

Here are the things I tried, each of way I tried at least 3 times already:

Call comstomer service, 

1, "your deposit have already returned and was cashed in xx/xx/xxxx, ", everytime i hv to ask them to check carefully, the deposit you refering is not mine, you did returned, but still $1000 havnt, pls look into whose are returned and whose hasnt.

2,"okay, I create a case for you" --  I called over 20 times and you have created 8 cases on the same issue! everytime they give me a case number and the next time I called, no one need that number, instead they creat another one.

3," your case is resovlved" --- one month after, recieved nothing. I called back again, they told me "we found your deposit is already returned and cashed......"  ---here we back to the first situation again.

4,"okay, let me transfer you to the xxx department"---- two mins later " hi how can i help u?..." exactly the same process, didnt help any.

5,"we are very sorry abt our mistake, I checked already and I can see your deposit have no returned, we will send a check to you shortly, and I will send you a email to confirm this" ---- nothing received, NEVER received any email.

6,"we didnt take your deposit, it is the store asked for, go to the store and ask them for it" --- I went to the store 3 times, someone there called the comstomer service for me and confirmed there is deposit in AT&T system and promised me send me check in a month --- nothing received.

7," there is no deposit made by you and your that friend"  --- I printed reciept on my hand!

the most funny thing is , last time I call , finally they transfer me to a manager in Financial department who seems very professional. He took half an hour to check my account, and went through all the situation from 1-6 above. then he said, oh yeah, we received yours and your friend's deposit. but we didnt recieve the other two! That made my mad,  after a while, he turned his point, saying, we didnt receive your deposit and your friends, back to situation 7. No matter how I stated I hv the deposit on my hand, he just repeat " as our system shows, we have returned all the deposit we had to you and they were both cashed".

Through the 3months' "fight", I dont know what else I could do?