I eat twice a day, ensure for breakfast and light heavy lunch, how come I haven't lost any weight?

Losing weight. To lose weight, get ur resting metabolism rate done(weight loss centers do this). This determines the total number of calories you need to lose 1-2lbs/week. Decreasing 500cal/day will give you a 1lb wt loss in 1wk; drink water (1/2 your body weight), eat small meals about 150-200cal 2-4x/(depending on your metabolism rate) and 500cal/meal at night: lean protein/veggies; avoid carbs, .
Balanced approach. Eating less may result in body storing more nutrients. Frequent small meals, if no complicating medical conditions, often better, as you become hungry. With increased moderate activity will likely be more hungry and can adjust meal size. Combination of protein, carbs, fat etc. Also important to get necessary nutrition. Can also vary diet to determine what works best. One diet doesn't fit all.
Make some life rules. Be careful about only eating twice a day - you don't want to give your body the signal that you are starving & slow down your metabolism! (then you'll never lose weight!) strive for low carbohydrate & high protein diet components. This takes a lot of study & label-reading to identify & avoid the carbs. By doing this, you draw upon your own fat stores for energy rather than using sugars you eat.