It sounds as if your son changed from Sport to M Sport if I’m reading it correctly.
Presumably there was a moment in time when it arrived and after the argument, he could have accepted the Sport?
I wonder what made the (admittedly useless) dealer change his mind.
But now it seems like a cut nose spite face situation.
I hope he finds another car he likes, the CLA Rene suggests is a good shout imo
2024 - BMW i4 Grand Coupe eDrive 35 Sport
2020 - Volvo XC40 T4 Inscription
2017 - Audi Q3 TFSi Sport S-Tronic