Tata Motors — Mileage issue

Purchased TATA ALTROZ XZ petrol on August 2020 from ROTANA MOTORS KOZHIKODE KERALA.My Car is having mileage issue, i already reported about this to ROTANA MOTORS KOZHIKODE many times.They just updated car software and clean the Air filter (2-3 times), there's no change in car mileage. Finally ROTANA MOTORS request me to check car mileage physically by filling up the tank.l, company had promised a mileage of 19KM/L but I am getting only 9KM/L.Total kilometres completed 12875, Vehicle number KL-11-BT-0012.