1. You accepted the offer no one forced you to
2. Do not compare your salary to thers, this is not professional from your side
3. Speak for your self and demand what you feel is your right
4. Be ready to accept the fact that your request can be denied
5. If you are ready to claim your right be ready to bear the consequences
6. Seek a job else where and when you find one quit with no regrets

Hope this helps

"The best way to predict the future is to create it".