Hyundai Motor India — fuel efficiency of the car

Address:

Rajkot, Gujarat, 360004

I bought grand i10 the mailage of the car as told by sales person was 17-18kmpl on highway and 15-16kmpl in city. I am only getting 10-11kmpl in city i complained every time when i service my car at hyundai service station but they told me in clear words that sales person dont know the true milage only we know it
Which means i am cheated by hyundai