Discover miracles

I am with discovery insure and I claimed because my car had a dent. They referred me to a panel beater who quoted a lesser amount if I use cash but when it is done via insurance the quotation is high. How can their approved panel beater quote differently if is cash? Is that fair business practise or my insurance are dealing with companies that are encouraging people not to claim but to use cash? I am confused because the last time discovery increased my premiums they said my car parts are expensive. When I claimed after my premiums were increased I was told that my car can only be fitted with pirate parts because it is out of warranty. I am discovering strange things with discovery.