No home on the range

THE distance range indicated on the trip computer in my 2008 Toyota Corolla Ascent is inaccurate. Every time I fill up with fuel the range indicated is 560km. I am a conservative driver, never speed, use a cruise control and travel mostly on freeways, and my indicated average fuel consumption is about 7.5 litres for 100km. With a fuel tank capacity of 55 litres the distance range should be 733km. The average fuel consumption has been reset many times, but the full range indicated is always 560km. The vehicle has been serviced twice and every time the service technicians have found no fault. Toyota's customer service hot-line informed me the indicator is a guide only and that a 24 per cent error exists. Do I really have a faulty range indicator? If so, how can I have this malfunction corrected? I know this seems trivial but for the money I paid I expect all vehicle operations to function properly.