I have a mitusibshi canter 2001 model engine.

Ensure Glow plug circuit is working correctly. This is the most common cause of difficult cold starts. If glow plugs are tested good, try manually applying battery voltage to the circuit to test if starting improves.
Were the fuel injection nozzles serviced/checked?
Test the engine compression.
Check for air in fuel system, likely to occur if there is a leak in the return lines allowing air to get into the system when engine is not running.