That's a horrible experience, link. You are certainly handling it well - never give up never surrender to the auto companies and dealers. They need to make this whole thing right for you.
At my local FLM dealer 10 or more years ago when I had a new Lincoln LS I brought the car in for something, cant remember what. When I went to pick it up, I found that the entire passenger side of the vehicle had been dented/scraped by probably a forklift. They say to me - it was like that when you brought it in. Luckily I was able to pull out the repair ticket and point out that the tech had, at my request, looked the entire car over and found NO BODY DAMAGE. So they were forced to repair that damage that someone there had done.
Lesson learned ALWAYS have the tech do an inspection of your car when you bring it into ANY repair facility.
I wish you the best with this issue and your Z.