Question about clutch damage in rental car

Hello, I rented an Astra combi from a car sharing company a few weeks ago and drove about 130 kilometers to an appointment where I picked up a bicycle. When driving out of the village the car suddenly didn’t pull any more and a strange smell developed in the car interior. Could just park the vehicle in a side road and then taught the car sharing company about the breakdown. I was then towed away. I have received a letter from the car sharing company, in which you ask me for the complete repair costs for the replacement of the coupling of over 220€. The vehicle was under one year old, but the Opel workshop claims that it would not be a guarantee, since the clutch and surrounding parts would have “significant” combustion traces. This is why they could prove “doubtless” that I handled GROB FAHRLÄSSIG with the clutch. Now the Carsharer wants to pass the costs on to me. I first objected to the whole in writing and have now received another letter that you had the clutch as a “evidence” in the company premises and still demand the full amount of damage. MY QUESTION: I have been driving a car for 15 years and I already had such a car of several times. I know how to operate a clutch. Of course, you can break a clutch even in an hour’s driving time, but I guess I would have had to pass the clutch half-way through the whole time and then full throttle or something. What are the possibilities for a clutch to break? I don’t know how all the previous tenants handled the vehicle either. I’m completely puzzled, at least, why I’m now responsible for such a crash. I did not treat the vehicle “grob negligently” and also not “negligently”. I just drove as usual! How do you like it? Would be very grateful for a few tips. Should I go to the lawyer? Gruss Camoranesi79