So sorry this has happened to you, especially after you'd saved so long for your car.
Do you have any legal cover on your policy? Based on this being a collision in England/ Wales (because that's the only legal system I'm familiar with, other parts of the UK and elsewhere are different) I would tell your insurers that you absolutely want to continue to dispute and are happy to take it to court (if you are that is). It will only go 50/50 if your insurers back down; tbh Land Rover drivers (especially if it was a Disco) are normally dicks (no offence to those Disco drivers who are nice!) so they will probably insist it's not their fault and not be willing to compromise. If their insurers don't offer a 50/50 and yours don't either it may well end up in litigation anyway.
Is it one of those cases where you say the other car encroached into your lane and vice versa? As although those are difficult to prove, things that can help (and it's worth telling your insurers if any of these apply) are
1. Which lane you were in as you joined the roundabout and why (so for example you were turning right at the roundabout so you were in the right hand of the 2 lanes which is marked straight ahead/ right turn)
2. The fact you were turning right meant you would have stayed in that lane until the exit before the one you were taking
3. Where you were going especially if its a route you know well/ travel regularly (even though you're a new driver, it's knowing the road that's important, so even if you used to pass through that roundabout as a passenger, you'll know it better than someone unfamiliar with the area)
4. Send them any photos you can of the road layout, google maps, streetview etc to show any road markings, your intended route and so on
5. If the other driver gave you their address and they're not local mention that too - they won't have known the road. Did they say anything at the scene about following their satnav etc?
6. Also whether you had any conversation with them at the scene or via text where they admitted fault in any way
7. Finally, the fact you're a new driver probably means you're more observant, careful and following the road rules way more than someone who's been driving for years, so again that should be something in your favour.
The main thing is just to be politely assertive with your insurers; remind them they've said the other driver's version makes no sense, so they should be defending this claim for you (or if you have legal cover passing it to solicitors to do so).
Hope some of this is helpful - if the actual circs are any different and you want any further advice just let me know
Finally although I know this is not much help now please get a dashcam in your next car, you can get them for about £25-30 on Amazon and they are so useful in these sorts of disputes.