We need more info about this vehicle............

1) What Year is this vehicle and Engine Code...........
2) How did you check the Glow Plugs............?
3) Did you diagnose to see if there are any fault codes in Engine ECU............?
4) Is the Earth Wire from Battery to Engine and Chassis is good...............?

 try and unplug the heater plug control module if it goes out that's your fault..