I'm in a very similar situation
I'm with markerstudy and my claim is being sorted by helphire.
Have helphire arranged for an engineer to inspect your car? I had one come and inspect mine and it was valued @ £884 minus the salvage. My car is/was a completely restored & immaculate Clio 1.8 16v, I only had it back from the respray for 2 months when the accident happened

The respray & restoration work counts for nothing in their eyes

Mine was very recently resprayed so you can imagine how p*ssed off I was to hear that

I managed to dispute the valuation by adding the costs of the mods on the car, suspension/engine upgrades/ 4 pot brake calipers etc. So I managed to get the value up to £1500 despite similar examples selling for well over £2k.
I opted for them to write my car off as I gave the prices for replacement panels from Renault main dealers (scandalousy expensive

) plus the labour costs that I knew from the initial respray. So whats happened is, my car is now a cat C write off
BUT I'm keeping the car and getting £1200 as payout, and it's being repaired at a cost of £500. So I'm £700 up on the deal

when they eventually pay up
Now as far as I can tell, your situation is exactly the same as mine - totally not your fault and it's not going through your insurance, but all against the 3rd party insurers negotiated by helphire.
Drop me a PM to compare notes if you like, this post may be clear as mud upon re-reading it

but tonight is my 1st night shift & my brain is mostly mush atm