Merit is not considered for govt job after written test..- interview due

Dear Sir / Mam, Sub : regarding recent recruitment for Nurse A and Asst. Nursing superintendent in tatamemorial cancer hospital, Dept. Of atomic energy. We applied for a central govt post in OBC category. We got the hall ticket and now call letter for interview. But recruitment cell saying that we are eligible for OBC posts mentioned in notification only. They are saying we r not eligible for general category posts only because ( recruitment cell saying ) we applied in OBC category. Recruitment cell also saying common merit will not be considered. In online application it was mentioned reserved and general type . We opted reserved because we belong to. No where in notification also it was not mentioned for separate category separate application. We will be diprived of wider opportunity if they dont consider common merit. They are considering communal merit. Obc posts 19 and general posts 38. As per them i will be applicable to 19 only only bcz i applied in obc category. Please give me good suggestion as it would be life changer to many obc candidates.