Accident claim

I was not happy/satisfied with how the panel beaters i was referred to send my vehicle to, I opted that naked give cash in leu so i repair my own vehicle, my panel beater generated a quote with Volkswagen parts prices using my vehicle vin numbers and the price on the quotation was higher that what naked appointed panel beater had quoted, Now naked say they had to pay me the amount that their appointed panel beater would charge them. why??? is it because its cheaper? How can i trust that their appointed panel beater is not using the **** parts. I feel taken for a ride here. please help.