Tata Motors — tata tiago vimal low mileage in city

I have bought tata tiago on last december 2016 around 3000 km driven till now and i'm not satisfied the city mileage it's comes 12 kmpl till now in city. I have made complaint in concorde motor ecr twice but not yet resolved they told in city depends on traffic if will give approx 11 to 12 only but when i was taken the car the sales man told it should give minimum 17kmpl at any traffic condition in city
Which one is true? I need proper justification and resolving the issue