Hi Christian
You need to be very careful here
I believe rear windscreens are no longer available and this might give your insurers a reason to write off the car
Maybe there are others on the forum who know of a source of rear windscreens?
I would suggest you check out local scrapyards to see if you can get one. You may have to get a specialist to remove it, at your risk.
I know your car has an LPG conversion which is a costly add-on. Is your insurance based on "agreed value". If not the insurers might offer you a derisory amount for the car
You might be able to get a settlement from them and then buy the car back from them and repair yourself, providing of course you can get a windscreen.it might even be better to forget about making a claim
Drawing from the experience of others you need to move fast. Where is the car, do you still have it or have the insurers taken it away? I would suggest you keep track of it before it disappears
Best of luck
Dave