A Cat N is a non structural total loss. Your rights are to have the vehicle repaired up to the vehicles market value. Insurers shy away from repairing fire damaged vehicle due to the safety risk for anyone in a bodyshop working on them. When burnt, plastic can give off Phosgene gas, which will quite literally burn through your skin and is carcinogenic. For some reason, these hazards do not affect salvage agents who dispose of said vehicles, or the people who purchase then repair them. Ask the insurer to provide a full engineer's copy of their Audatex estimate, if the repair cost is less than the market value, and you want it repaired, insist they repair it. They are under contract to do so, do not listen to what they say, stick to your guns.