AED 500 fine for no mistake

ived a fine amount of AED 500 for the reason that my vehicle broke down on the Al Salam Street near pineapple building on 16-03-2018 (Friday). There was some unknown substance on the road because of which 4 other vehicles broke down. Police came to the spot and were not able to trace the thing and helped us move the vehicle using towing service. On request, they did not provide us with any report of the incident. I was driving a rented car from Shift Car Rentals and they insisted to get a Police report else all the charges of the damage would be on me. Hence on 18-03-2018, I went to request an incident report from the police. The officer did investigate and told he is going to mention that I had hit a substance. I said it is fine and he proceeded with the report. I was never told that I would be fined for this reason. It is not my mistake that there was something on the road which even Police could not find when they had come to help us. I do not know why am I fined for no reason. Kindly assist.