You didn't specify which exam result you are talking about. If you have kindly specified the exam then it will be easier to provide you a satisfactory result.

But in general this kind of problems aren't seen that much. I will request you to check the rank card properly and recheck if you are some how overlooking something or not. If you are not then do check the application form and check whether you had added the caste or not. There is a probability that you forgot to put your category. So just check it. If all this are ok then do try to contact the exam authority regarding you problem and I hope they will get back to you as soon as possible.

Hope my answer helps you. Have a great day!