No ownership and integrity from Toyota SA

Bought a Hilux 2.8 DC new in 2018. Realized later that the navigation system is out by 100 meters when travelling at speed. After many attempts by Toyota the couldn't fix it and admitted all models from 2016 to 2018 had this characteristic which is not conforming to standards. They replaced it with a 2020 spec radio and the gps issue was fixed but the rear speaker sound disappeared. They indicated that they are not going to look into the matter further as they tested the decibel readings in the front of the vehicle only and they say it conforms to spec. The sound quality of the vehicle has been severely compromised by this defect.