Avis does not want to pay back my deposit

Avis does not want to pay back my deposit, it's been more than 7 day since I returned their car at their Green-acres Branch in Port Elizabeth. I have been doing a follow up with them and being told that my contract is closed and finance will be making the payment soon. The week ended with them telling me the same story yet the money was not processed. On Friday they promised to get back to me but no one did. This morning when I called their head offices I was told that my contract number shows that I only hired for one day and not two weeks and it now shows that my contract is void and therefor can not track the payment of my deposit. The lady that was assisting me at the PE Branch Monique is not available and has not returned any of my calls.

Please assist me. kind regards **********