Another classic example of how un knowledgeable the main dealers are on these cars. Do not give your car to a main dealer, its been said soooo many times before. I gave my 350z to a main dealer years ago and asked them to just put it on a ramp and refit a rear vacuum hose on my plenum, 10 min job. I called after 3 hours and they said they were working on it still. Tried to palm me off with a bill for £360 + vat. I stormed in there made a scene, gave them £30 and demanded my keys back. Suffice to say I got my car back and vowed NEVER to use a MD again.
The lot you used should be shot. I would insist on my money back based on wrong diagnosis and bloody neglect for not refitting bolts. I would demand my money back or go to OFT.