HIRED A CAR AND NEVER GOT MY DEPOSIT BACK

I hired a car at the Avis car hire in CPT airport last year and when I came back I returned the car to them they never deposited my money back.Now I went to their offices several times and they told me that they will deposit the money back to me.The last message I had from them they said the money was deposited to my account but it bounced back.Now again I tried to make a follow-up last month they told me it is an old issue and it shows they paid the money back to me.