Bad information....advantage takers

My mother bought a nissan magnite last year on the 06 December 2024.Everything was spoken on the phone however they never gave her a full spec sheet anout what the car came with an what was not included in the package deal.The car came without a radio,this was never informed to her..they just inforher on delivery day..now since the infotainment system cost roughly R6500 from what they were quoted..however now they told her that she must pay half of the price so that the system can be installed.What i don't understand is that they were at fault for not informing her the first day she said yes to them.And we where told that if we were to install an aftermarket infotainment system it will void the warranty so now am confused with the "Gazin nissan dealership "