New 2017 Model Poor millage in diesel engine..

I Have Purchased Xcent New Model Diesel CRDI 1.2 ltr sedan car few months ago. I driven 5200 km in my car. The Performance is Good. But, MILLAGE is Low. Highway Millage is 19 km/liter without AC. Suspensions are Good, Back Spaces is very good. Boot space is good.. the Hyundai Company is there's not good solve the millage problem...