Strange. My cousin went for fill up in his PKDM Alto. A FX cab was ahead of him. When they started filling, they filled gas worth Rs. 1200 in his FX 55L cylinder.
Seeing that, my cousin decided not to fill after 2 hours wait in line, as at this rate, he found petrol to be more economical.
As per wikipedia, 1L ~0.55KG for LNG.
Either the pumps are showing fake pressures and filling lesser than full cylinder capacity for you guys, or that particular pump had a fraud meter.
Things will be clear once you consume the full tank and know the mileage you got for around Rs. 600 fillup