Poor work done.

I had an accident and my car was taken to their workshop. Insurance authorizd the claim. And they ordered the spares or rather should I say the parts that was damaged on the vehicle. On the 4th of March I went to collect the car, on the 24th of March while driving, the bottom engine cover came out and caused some damages on the car. I noticed that the *****s that they used to fit the cover back was not the right ones, actually was not even the ones that came with the car. I also have a question that is not answered. Are they even authorized to work on Audi cars or the towing company just doing a brother a favor by taking cars to his workshop. If ever they were the authorized or approved Audi repairer they should have known better and do a proper job. I now drive a car without a belly plate, left fender liner which caused some electric components exposed. Now I'm waiting for them to fix the problem which they caused because of their poor work performed on my car. on the quotation it showed that the new engine bottom cover was there but was not ordered instead they fitted the old one which was badly damaged due to the accident that happened. From my experience insurance don't allow parts to be repaired instead they replace with new once. But it was a different scenario in my car. They replaced the old parts and try to fix them and use wrong *****s to fit it back which caused it to come out because it was not properly secured.