VEHICLE IS NOT GIVING CLAIMED MILLAGE

Location/place: UDAIPUR

Name of company/service: K.S. FORD , UDAIPUR

DEAR SIR,
I HAVE PURCHASED FORD FIETA CAR ON 24 TH OCT 2011 FROM M/S K.S. FORD UDAIPUR .ITS CATALOG SHOWS ITS MILLAGE AS 21.37 KMPL.IT WAS NOT GIVING THIS AVERAGE SO I HAVE GET IT CHECKED BY M/S FORD. WHILE CHECKING BY THEM IT CAME 15.71 KMPL, WHICH IS NOT AS THEY CLAIMED AT THE TIME OF SELLING.I HAVE MAILED THEM FOR COMPANSATION FOR THIS MILLAGE DIFFERENCE , I DID NOT GET ANY RESPONSE.
CAN YOU HELP ME FOR GETTING COMPANSATION ?