Peter,
Have you spoken with the owner/manager of the place yet? I can't believe that whomever you were speaking with put you off until Tuesday unless he/she didn't want other people finding out about their fuckup. Me, I'd be livid as well. But don't expect them to offer all that much in compensation, they're in an insanely tight-margined and heavily competitive business and they are probably already figuring that they lost you as a customer so there's not much left for motivation for them. I'm not saying they don't owe you something but just offering a perspective that I've been faced with as well. If it were my business I would have had you in there as soon as I found out about the mistake and done whatever was necessary to a) put your car in a safe and drivable condition even if temporarily and offered one hell of an apology.