Look, you need to understand that these sorts of things are negotiable. Sure, they use calculators and sums to arrive at a number but do you really think the deal they offer you is the best deal they could offer you?
You need to think of it as game. Take insurance for instance. You need insurance, you call for quotes. You pick the one you like and ask for money off. Do they give you it? They might, but probably not because they've had to give you a good deal to get you to pick them over their rivals. I'm not saying they're not making money off you but they're trying to keep the price keen, if they want your business.
You write off your car and now need them to pay out. This is a completely different situation. They already have your money. They are not that interested in getting you to stay with them next year as you've just demonstrated that you're a liability and statistically you're quite likely to crash again. So do they offer you the best payout they can? No. Never. Why should they? They have no incentive to give away money they can just as easily keep. So you need to have a little fight with them to get them to give you more money.
In some situations the price of something is not negotiable but it's actually rare. We Brits just don't haggle, it feels rude. Other people do it all the time. I've saved hundreds of pounds on things just for asking. Maybe they won't give you a better deal, but ask. Make a counter offer. At least try!