Toyota Fortuner 2.4 GD6 Fuel Consumption Problems

We bought our Toyota Fortuner 2.4 GD6 almost 2 years ago. A few months ago we noticed that the fuel consumption was not as usual and we took it to Middelburg Toyota where they checked the injectors and computer. The consumption is still not right and we get between 4.5 & 5km/L. This is ridiculous and we might as well drive a V6. We contacted Toyota on numerous occasions with no avail. They do net get back to us to resolve this issue. My husband drives a 2.4 GD6 Hilux and he average between 9 &11km\L. Both have the same size fuel tank and when my husband fills up he gets over ****m but when I fill up I only get about 430km. The gauge will be on quarter then the range would be on 7km. I have pictures to proof this. Then suddenly it will say "REFUEL" but the gauge is not even close to empty and the light not even on yet. The next day the range would say 38km with the gauge almost on empty and the light on. Then suddenly the light goes off and the range say 33km. My husband disconnected the battery one time when it said "REFUEL" but the light was not on and when het connected the battery again, the range was 48km. We contacted Toyota again and they only informed us that we must fill up about 3 times (+-R5000) and keep the slips, then only will they look at the problem. This is utterly unacceptable and costing us lots of money spent on fuel.