Civic Exi has a great fuel average....i myself got 18+ a num of times on motorway from isb to fsd/lhr (brim to brim method)..speed was 90-100 km/h...at some places 110 as well...however if you keep speed 120km/h with AC , the average drop to 15km/l...but in no case less then 15km/l till the time you ate driving as per motorway speed limit.
SO I STRONGLY BELIEVE YOUR MILEAGE
SHEER HATRED FOR PUNJAB POLICE