If you are doing the aerobics and maintaining a strict diet but still could not possibly get the desired results, then you must think about increasing the intensity of your exercise. Aerobics is not only about dancing to the tunes or practicing some movements, it is about sustaining your heart rate at a desired level for over a period of time.
Aerobics sessions should be made longer. It should last up to atleast 1 hour and during that time your heart beat should be maintained in the training zone. For that your heart beat has to be checked periodically. Maintaining your heart beat in the training the zone for about 30 – 60 minutes will definitely burn more calories and will help you to get desired results.