You can stress about this and spend a lot of your time chasing down someone for repayment. This is the wrong approach IMHO.
Instead just sure in small claims court (limited to $5,000). This is done without lawyers. You simply present your lease agreement, bank statement and any relevant communications.
Once you get that judgment give it to a collections agency and forget about it. The agency will take a percentage of anything they collect.
Then just look at anything you get back as a bonus.