Why is Dotsure allowed to bully their customers when they make a claim?

I have received the worst claim I ever thought possible. First they offer me half of the retail amount it was insured for, with all the necessary depreciation accounted for. After the ongoing fight the adjusted it a bit. Tired of fighting I accepted the claim and opted for the cash in lieu, to keep my car and fix it myself, but they now insist they want to take ownership of my car, that i must sign and change the car ownership to them. Is this even legal? They call me and tell me I have 7 days to make a decision, after which it they will put the claim on hold and will re-open and continue when I contact them, with no negative impact on, telephonically, but send me a horrific rude letter and an sms-es that say if they do not hear from me within the 7 days given they will cancel my claim without any notice whatsoever, and conclude that I want the claim canceled. Would you believe it? I have raised this with them, but on the telephone they speak nicely but in writing they say quite the opposite. Please help me understand why they want to exercise what they do with claims where they keep the car and pay the customer out completely. I am keeping the car and paying for it and will use the difference to fix the car on my own?