B.A

Talk to school administration or register for correct course.

Yes, you are. You can fill all type of exam forms. IGNOU is UGC approved and accepted by every exam conducting authority.

Hello Uday,
I can understand your angst for missing 50% mark by just few marks. But do not worry. Many universities allow students with 45% marks to appear for entrance exam for admission into PG courses. For NEHU, unfortunately I couldn't locate any such restriction. However I am attaching a link that will give you all the required information about NEHU and also helpline number.
https://nehu.ac.in/Admission-2018

You need to get in contact with the Examination Controller office of the University or the Subject Department of the course you did.
If it is a regular degree, then the concerned institution under that university will give that to you.

No, you cannot. Calcutta University or Jadavpur University doesn't allow a Masters unless you have a honors degree. However, you can try distance education in mass communication.

Any graduates studied in 10+2+3 pattern can do MBA/PGDM with valid entrance score.

Both programmes M.A. & MBA are different. For admission in M.A. you will get it easily but for M.A. you need to score good in the exam and crack GD/PI, a well conducted exam by college. All the best.

Why not? You can easily do MBA after graduation from any stream. Stream and specialisation doesn't matter. You need to crack the entrance exam conducted by management colleges of association.

Minimum age should be 17 years as on October 1, 2018 for this year's admissions. For more detailed analysis of the exam, you should visit:
https://www.google.co.in/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/university/jawaharlal-nehru-university/exams/amp/jnuee&ved=2ahUKEwiQ2dv_1bncAhVDuY8KHcZQCmMQFjABegQIARAB&usg=AOvVaw04muoFUzmrNsC4NIAbONRl&cf=1
Best of luck.