Insurance companies are in the business to MAKE MONEY! They do not care about the QUALITY of the work, as long as it LOOKS good on the outside.
I am currently fighting the body shop and insurance co for some repairs to a right-rear fender. The car is dark blue and the fender is sea-foam green with a half-assed coat of dark blue sort-of covering the green. The insurance guy looked at it and said it looked fine to him! Of course HE would say that. If they have to pay for it to be redone, THEY LOSE MONEY.
Best suggestion for you is go to the insurance company and stand on the table and jump up and down, screaming at the top of your lungs until they fix it to your satisfaction or lock you up in a padded cell.
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles