Bad Fuel Economy with Hyundai Santro Xing GLS LPG

Bought the Hyundai Santro Xing GLS LPG in December 2008  The only reason to bought this Santro ECO was the LPG kit, by thinking that to reduce my fuel expenses. But the out come result leads me absolute disappointment. It returns between 6 and 8 kms/lt in the city and 10 kms/lt on the highway. These figures are very very far from the given Hyundai Santro Xing GLS LPG prospectus. Before I bought this, I compared with WagonR Duo, by personally and by taking views from users and experts from CARWALE.COM. Even though I bought this because of brand name and faith on service of HUNDAI. But I duped and after I bought this car only I could realised that how much mistake I made. I know HUNDAI is a successful car maker, but not LPG car. Comparatively VAGON R Duo is giving better mileage in the city as well as on the highway!

And the surprising thing is, here in Bangalore, no service center, either TRIDENT or ADVAITH, wasn't ready to take this as a complaint. Even they didn't have the KIT to check the mileage with LPG. They are simply put their hands up and telling that they couldn't do any thing with LPG mileage and there is no answer, how to improve LPG fuel economy. These service centers are thinking that the service means, water wash and changing engine oils. They don’t bother about the other things, particularly when we went for free service. The customer care cell is also not bothered about the same. There is no response from them. WHAT TO DO?