Maruti Suzuki — Poor mileage issue

Address:

Chennai, Tamil Nadu

Maruthi Ertiga purchased on 10/01/2014 in chennai bearing registration no. TN10AP 0886. The car ran for 4300 Km for the whole year. During 1st free service vechile clocked 14 KM in high way. in city around 10 KM .
During 2nd free service vechile clocked 12KM in high way. in city around 10KM
During 3rd free service vechile clocked 9.7KM in highway.in city around 10KM.
After 3rd service we took the vechile from Chennai to Srivilliputur To Chennai.
during 1st tank fill of 45 liter car clocked 360 KM (average speed in high way 100 to 110 km)
During 2nd tank fill of37 liter car clocked 359 KM ( average speed in high way110 to 120 km)
During 3rd tank fill of 36 liter car clocked 365 KM. (average speed in high way 90 to 110km)
speed ranging from 90 km to 100 km odo meter average mileage shown 10.2 km
speed ranging from 100km to 110 km odo meter average mileage shown 9.7 km
speed ranging from 110 km to 120km also meter average mileage shown 9.7km.
After returning to chennai car taken to our nearest service OMS Maruthi service station in Madippakkam. they have checked all spark plugs, air pressure in tyres. After setting we have taken the car upto vellore from chennai for a high way ride. the car given 12.7 km at speed range of 80 to 100 km. it seems to be some technical issue in vechile. OMS service engineer suspects the clutch plate assembly. The car driven by self, my earlier Maruthi 800 served upto 1, 20, 000km. with best mileage of 16 to 17 in high way.No clutch plate change. Is it the condition of maruthi latest vechile, pl. clarify and do the needful.