If you’d have ordered in or before June 2020, he could explain it away – that’s when the facelift happened, including removal of the reverse camera as standard on the R-Line. Could’ve been an honest mistake at that point in time. A year after the facelift however, if he indeed falsely advertised an option on the car, i’d certainly try to get some form of compensation, or walk.
There’s potentially the option of adding it after it’s being built (retrofitted), but that’s going to be considerably more expensive. If you can somehow prove/convince them that they falsely advertised the camera, they might cover the cost (or at least half of it).
This, or walking, are your only real options. The car’s removed from the scheme, so there’s no re-ordering it.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.