Honda Cars India Ltd. — Mileage issue in city

Address:	492001
Website:	Honda customer care

I am honda city car since 2.5 yr with a total run of 15000 km till date. Its mostly in the city. Initially the mileage was 9 km which increased to 10.5 km after 1yr. I am regularly doing services & i am good at driving. Now the average dropping to 8.3 km. I asked the show room person. They say everything perfect. But how it's possible. Do something. It's a serious issues against claiming 15;km by company.