AVIS ********ly retaining deposit for car rental

I had a horrible experience with Avis (Lanseria). I picked the car up from Lanseria airport at 22:00 on 21 January 2019 and paid the rental as well as a refundable deposit. The car was not inspected by anyone from Avis when I collected it. I returned the car three days later on the 24th of January 2019 and the Avis employee told me that there was a scratch on the car. I made it clear that I have not caused any damage so he gave me a form and advised that I should just write a short summary stating that I returned the car in the same condition it was in when I collected it and that no inspection was done by Avis upon collection. I wrote the summary and signed and then saw that the document I was signing was a 'Damage Report'. I asked him if this report will now result in damages being deducted from my deposit because I was concerned that I will now be penalized for damage that I did not cause. He assured me that the full deposit will be refunded within 2-3 business days. I waited 6 business days before I phoned Avis Customer Services to follow up on the deposit that was supposed to be refunded. Customer Services then advised that the car was billed for damages. I told the person assisting me that I had not caused any damage to the car and that I was informed by an Avis employee that the deposit will be refunded within 2-3 business days. I was then referred back to Lanseria branch and was then assisted by Paul, who explained to me that the car goes through 3 quality checks before it is collected by a client. I told Paul that no one inspected the car with me when I collected it, I was merely given a key and told to get the car at parking bay number 8 so they can not, after the fact, allege that I caused the damage and deduct it from my deposit. Paul advised that they will do an investigation and look at the previous reports on the car, if there's no mention of the scratch in the previous reports, I will be billed for the damages. If not, my deposit will be refunded. In other words, irrespective of how the damage was actually caused, I will be held liable if the damage isn't mentioned in a previous report. When I asked him how it is possible that a week had gone by and they're only doing this investigation after a client phoned and complained, Paul simply advised that he was not the person dealing with the matter., but he will get back to me. This conduct of Avis not only amounts to despicable customer service, but is in contravention of the Consumer Protection Act. Avis is now leaving me with no other option but to incur further costs to institute legal action to claim my deposit back as I can not be held liable for damage that I have not caused.