How much did you pay and how new is the car?
Do you still have the ad?
Do they deny it was there?
There is case law that relates to misdescriptions that says that where an item is not sold only by description then the presumptions do not apply.
However, that was before the new Consumer Rights Act and anyway relates to the SGA rather than misrepresentation.
Clearly there was a misrepresentation. Whether you should have noticed or not is entirely a different matter. It seems to me that it would have been more useful to them that you did not notice this if they were saying that it wasn't said. Then it would be a problem.
If they accept the ad did say that there was a camera and there is not then that is misrepresentation.
You wouldn't be able to recover the entire cost of the vehicle but you should be able to recover the diminution value.
Can I clarify anything for you?