Had the same scenario with my Merc' a few years ago when it got rear-ended on the M25.
Three week repair turned into six, helped by the fact that I wouldn't accept the car back until they put it right, i.e did the job they undertook to do properly
Basic repairs were actually fine, but the re-assembly was, well lets be honest - a bodge job. Same thing, screws / bits missing, putting back cracked / damaged fittings with a dab of glue here and there (but claiming new ones of course!).
Scratches on the front of the car that weren't there to begin with....... it went on and on.........(TIP:- Always take pictures all around the car before you part with it).
Refused to sign the car off on no less than 5 occasions!
Eventually an insurance arbitrator was called in, who (thank heavens) basically told the shop they were taking the p!ss and to sort it.........plus the bill (their bill) for the hire car I had was getting VERY big........(well £3000 big actually!).
Body shop owner eventually told me....(Quote)....."The trouble with you Sir is that you know too much about cars for your own good"
What the hell sort of statement is that?
If you have a substantial shunt and you are blameless
then consider a no win, no fees claims solicitor - they can
work in your favour rather well - just be careful who you choose and get the 'No Win - No Fee' bit in writing. I was very pleased with the one I used, clearly knew what they were doing and they didn't charge me a penny.
Quite frankly I'm endlessly amazed at the condition some of my associates accept their cars back in.......bad colours / ruddy great gaps in the panel fit / broken bits stuck back on - the list is endless.
Whatever happened to the days of doing a 'proper' job for the money?
Alien concept nowadays methinks!