We knew it was missing. If you had it and lost it then that's one thing but if you are sure you never received it then that's another. In which case I'd have thought you could take it to the claims court.
Meanwhile why can't they replace it with a working disc without the cao ? Mind you without one it'd be difficult to use it to install and register. But if all you are doing is repair you might be able to get the existing registration number from your PC once it boots up again.
Another thought. Can you not borrow a working disk from someone ?