How do I get back my money after a dealer mistake?

I picked up brand new Renault Koleos in July with a complimentary full tank of fuel. On the drive home the car was jerking. I contacted dealer immediately and was told to get the car towed to the workshop. He mentioned that he hoped they had not filled it with the wrong fuel. After checking the car they told me they had put petrol in instead of diesel. They flushed out the fuel tank. Concerned that this might void the warranty, I contacted Renault Australia by phone, and was advised that as it was not a manufacturer defect, rather human error, that the warranty was void. But I received an email from the dealer that he had contacted Renault and that the warranty is not void. I asked for this to be put in writing, but they failed to do so. I then contacted Renault again and told them about the dealer’s email, but I was told that they had received no correspondence from the dealer. Renault Warranty Department and Customer Service officer emailed me that in future any issues with car relating to wrong fuel, warranty will be questionable. Renault had also cc'd the dealer in this email. Dealer has not responded to my email or letter of demand. I have invested a huge amount of money and time in relation to the purchase of this vehicle and I have not had a response from the dealer. According to the Information and Maintenance book from Renault 'What is not covered' it states, ' Use of inappropriate fuel'. Can I get a full refund as I have a brand new car with questionable warranty? The car is still with the workshop. Please advise how I can get back my money?