Hero Motocorp — duet and its service

I am driving duet for 4 years.
But from first day its having some or other problem.
Engine oil finishes or runs out very fast inspite of regular service from very first day.
I have told the problem to the service man alot times but no outcome is seen.
Due to this problem once my scooter chocked and i have to drive it home by my self.
Due to this whole engine was opened and many parts were changed mainly the piston.
After these changings, the problem didnt finish.
There is no sulution dispite of being in warranty. But after warranty period what i'll do.
Now whenever i drive it, the only thought comes in my mind is that it doesn't stop in middle of road.
Now i want a permanent solution to this problem and scooter.
I am very irritated and fed up of this scooter.