Assessment and Claim

I was in an accident on 16 Dec. Herewith in short what happened: I stopped at a T junction I wanted to turn left. There was oncoming traffic on my right hand side and I had to wait for the traffic to pass, before turning. I looked to the left when the traffic was clear from the right hand side and saw the truck which was parked on the pavement started to reverse. In a state of panic I tried to put my car in reverse in attempt to avoid been run over by the truck but because I was in shock I stalled my car and before I could restart the car, the truck hit my car on the left hand front mud guard, destroying my mud guard, front bumper and head light assembly. I had no idea that the truck would reverse. Santam just decide that I am 20% guilty in the accident and they just make adjustments on the quote that I send without an assessor that assessing my car. How could they only assess on pictures taken? I'm also insured by Santam but they only pay me out 80% of what they decide the cost will be to repair my car? Why am I insured at Santam, with excess cover but Santam decide that from an amount of R27000-00, they only pay me R15 000-00?? Do you think that is fair??