Wow, so sorry to hear this.
Your experience sounds completely unacceptable. Aside from never trusting your cars to them again, I would be looking to write formally to the MD setting out the timeline, and your concerns with suggestions as to how you might be compensated financially for your loss of time and the damage done to your vehicles.
I would also copy in Porsche UK customer services so they are in the loop should you need to escalate further.