Nexa — baleno delta 1.2purchased baleno

Address:

Ghaziabad, Uttar Pradesh, 201002

Purchased baleno delta car from next showroom of magic auto, dwarka on 29/01/2017. Right from first service onwards i am raising the issue of low mileage of the car. So far two services are over. Car has run 10078 km and iiird service is due. The car is giving a mileage of 8-10 km per litre of petrol i repeat 8-10 km per litre of petrol. What is the reason??
Is there any one in nexa maruti to redress the issue or i must approach consumer forum for selling substandard car.