I agree that's not enough food. When you don't take in enough calories, your metabolism slows way down, to compensate for the lack of incoming calories.
Protein and fiber will fill you up more quickly and keep you feeling fuller longer. Fill your plate, mostly, with veggies, and portion of lean protein, then add a serving of grain and other nutrients.
Exercise is essential, because it builds muscle and muscle burns fat. Aim for at least 30 minutes, 3 days/week, but an hour/day 5 days/week is best. Be sure to add strength training along with aerobic exercise to get the muscles built up to burn fat.
By eating only 500-700 calories a day you're putting your body in to starvation mode. It's not healthy and will not help you lose weight and may lead to you becoming malnourished.
You need to be eating double that (at least). Ensure you get a full and varied diet with all the essential fats, vitamins and nutrients.
When your body goes in to starvation mode you'll did it increasingly harder to lose weight. The body sees any food as precious and stores it as fat so in fact you're doing more damage then good.
Increasing your food intake and upping the exercise will really help. Unfortunately it takes a little while for your body to come out of starvation mode so be prepared for a few months of hard work
Good luck with your weight loss