I10 mileage is very bad

I purchased this i10 sportz 2013 model, this is my first car, I feel very bad to buy this car, it is giving very bad mileage 6 to 8 kmpl. For maintaining this car I need to buy one petrol tanker behind this car. Before buying this car I saw the reviews every where mentioned that it gives 17 to 19 kmpl, the person sold me this car also said the same. Later after driving this car I realized that all are lies. I am trying to improve the mileage by service and changing the necessary parts. If still giving bad mileage I will keep this car a side and use my bike. Very very bad mileage, and I am taken worst decisions to buy this car. Style , comfort, space is very good but mileage is very bad