Avis not paying back my fuel deposit

On the 16th of February 2015, we returned back our hired vehicle to Avis, with a full tank of fuel. Vehicle was rented via Outsurance and a fuel deposit of R1350 was paid over to Avis, when we initially collected the vehicle. We have tried everything to get Avis to pay us back our fuel deposit, but with no luck. We will revert this matter to Outsurance Executive and their procurement department, as well as the Financial Ombudsman. Thanks Avis, for causing us a headache and forcing us to go this route.