Agreed, that's a low value!
Try replacing
your Type-S for that money - no way!
Sam paid (more/around that? for his, IIRC

) and when he bought his, correct me if I'm wrong but it wasn't in as good nick as yours (all the little niggles rapidly sorted of course!)

Heck, even that one with the knackered clutch bearing is up for more than that at the moment!!!
And as for Cat C? That's absolute bollocks, can't believe they've done that!
Not withstanding the PITA for a VIC check (£ and where is the nearest centre to you?) the Cat C goes on your V5 and will affect future value of the car.
Description of the categories below (from a salvage company);
Cat A is for burn outs and gutted vehicles or when the vehicle has been involved in a serious RTA that has been subject to a death and also 'contamination' issues such as 'human tissue' in the vehicle....... Only value is in the baled weight at a metal recyclers.
Cat B is where the vehicle is no longer safe to put back on the road and must be broken or crushed. These can only be sold to registered dismantlers with an EPA waste licence. They are actually sold as parts and are no longer considered as a vehicle. There is no economic consideration involved, purely a safety one. Vehicles that have been flooded are normally written off as a cat B.
Cat C is where the car is repairable but is not economic to do so. Think older cars and or ones where the chassis needs jigging.
Cat D is where the vehicle is repairable and would be economic to do so (cost of salvage + cost of repairs < Pre accident value) but the insurance company has decided not to repair the vehicle. This could be due to excessive storage or recovery costs, etc.
The actual Association of British Insurers guidance note is
here
Reckon your insurance company/claims handler/assessors have been complete arseholes tbh and I'm sorry for you

At least it's sorted though and you have your car back and the means with which to fix it.