Not as fuel economic as advertised

Hi I bought a cherry red astar vxi in august and I have covered over 4000 kms and this was an okay upgrade from my previous alto. ride quality and comfort and everything else about the car is good but the mileage is pathetic and attrocious. Being an old fashioned guy I did not cross over 60 kms and changed my gears at the recommended speeds untill over 3000 kms but now to my surprise I am getting a mileage of only 13.5 in the city with 60% usage of the ac. Having previously used an alto i had my trust in maruti but they have let me down and I am now starting to regret buying the car. cars with bigger and faster engines like the i10 1.2 or the swift and beat are giving more mileage than my astar. I dont know if anybody out here has faced this similar mileage problem with this car. with the high rise of fuel and the complete disappointment of maruti I am now contemplating of changing this car for another one. this car was purchased from khivraj motors at mount road in chennai. I would understand if I raced with the car or drove it like a maniac and screwed my engine but I have not and this is very disappointing and a complete regret.

Everything else about the car is good and a value for money excluding the mileage factor. 

I hope that maruti stops cheating people by misrepresentation of facts. Please let me know if there's something that i should do about this.

Quite spacious for a small car, good ride quality,good features and smooth engine rideLess mileage