1. Kajang belongs to Selangor state, Cheras belongs to Kuala Lumpur. Based on my understanding, if accident happen to Selangor side, shall report to Selangor Police traffic department. Same for Kuala Lumpur one. Kuala Lumpur dont handle Selangor case. Need someone to double confirm on this.

2. Do you take down evidence? E.g. photo of incident happen, their car plate number and ur car plate number... video or picture of how the incident happen... bang which side of ur car, thn where does the opponent car came from and bang into ur car etc. Yes, report police is  a must but clear explanation of how the accident happen, and picture of the scene plus car number that bang u would be required to proof and able for the police officer to assist u up...