AOA Sir!
There are 02 possibilities:
The Sensor beep is disabled which as per my info can be disabled. a friend in his V8 2009 LC hit a farm house light pole while reversing and not seeing the camera.... he regrets that he had disabled the sensor alram / beep indication. Might be sensors would have been disabled.
some times the damaged bumpers replaced by car dealers. or the non OEM Nav units do not support it.....
I think you are from Bahawalpur if i am not wrong.... During any upcoming Lahore visit you can check Arif Electrician in Faisal Town (Kotha Pind Red Flats) or Jamal Electrician (adjacent to Tracking world Faisal Town C block Market / opposite to KARADOs ).