Avis is denying and holding my deposit

I paid a deposit of R2750 in August and R603 had to be deducted for fuel and be refunded the balance.I returned their car on the 10 September but until today I havent received my refund.Head office is denying this deposit and I have sent them bank statement but still they are not refunding me. I have sent many emails to them and have been to Amanzimtoti branch where I did all paperwork and payment of this deposit but they also don't assist in any way except that they tell me that they have sent email to their head office and will contact me which they don't do until I go there again to get the very same ewsponse