Hyundai — Mileage is very poor

Address:

Chennai, Tamil Nadu

Hyundai i10
we got a hyundai i10 last year.The company had promised that the car would give us mileage of about 13-14 in city roads and about 18 kmpl for travelling on highways.
But we have never got that much mileage at all.Ours is a Kappa engine
we are getting mileage of about 7-8 kmpl.. we are very disappointed.Kindly advice us as to what to do.The car is still under warranty period