It doesn't much matter how accurate your calorie estimates are. If you estimate that your daily caloric requirement is 2500 and you're eating 2000 calories a day, then you should be losing about one pound a week (1 pound of fat = 3500 calories). If you find instead that your weight is remaining constant, then either your caloric requirement estimate or your caloric intake estimate is wrong (or both are). In either case, your only option is to eat even less, per your measurements.