Dear Sadiq,
Here you need to realize that more information is to be collected on your part -
1) What does your appointment letter say regarding working hours.
2) What does your JD say regarding your profile.
3) Does the HR has any policy manual regarding the working hours and Over time rules.
Please collect the above information and then speak with your reporting officer.If not satisfied by his answers, then discuss the issue with HR.
Please remember that your behavior while discussing the above issue should be polite and in a courteous manner as the subject matter is sensitive. By proper discussion you will be able to change the situation around you.
Regards,
Ashishkumar