it sounds like they have already made up thier minds

tell them that you do not wish to drive the car in it's current state and can they arrange someone to come and have a look at it where it currently is

don't hand over any documentation

don't give them the car

once there is an offer, in writing, explaining your options, then decide whats going to happen

you will be able to keep your car as salvage if it's total lose
you'll be able to hand the keys over if you want shot of it
you'll be able to get it fixed if they offer that service

when i wrapped my saph they came and collected it to be inspected, with 2 wheels missing and every panel bent there wan't much arguement that it was fooked and i got a cheque through the post 2 weeks later
when i pranged the granada the 3rd party insurers paid out so it's not been recorded by my insurance company as being written off so i get to keep the car with it's bent rear end