Working at the same Govt Post for three Years

Sir/Madam, I am an officer at the asst grade level, Group B in Indian Railways. While doing my duty, I was also made in-charge of handling another Post of a much Higher Degree, i.e. Senior Scale Officer Level. The person working as the Senior Scale Officer retired, and I was ordered to handle this post as an ad-Hoc. I have been handling the responsibilities of this post since almost the last three years. I have been appreciated in written by the highest authority of our office, which says that I have been working diligently while saving Railways a lot of money, which would otherwise would have to be paid as Salary to the Senior scale officer. It may be noted that as I am handling the Post as an Ad Hoc Officer, I am getting paid my original Salary of Group B level, and no special incentives etc are being paid to me. The post is that of Sr.Media Officer and while working at this AD Hoc Post, I completed a correspondence PR Diploma from open university. Now, a vacancy has come up at the Head Office for the Post of Media Officer, and I planned to apply there. I want to pursue a Court Case over the issue- Since I have been working at this post as AD Hoc for three Years, I should be posted as Media Officer permanently and actually receive the Pay Package of a Media Officer. I also have the requisite qualification needed for the same. Will I Succeed? Should I go ahead with the case? Also I will complete three years at the Ad Hoc Post in November, but the vacancy has come out now. So Should I go ahead with the court case now or wait for the next Vacancy Announcement-which might be next year or after two years! Kindly Advise. I need to be sure that I will win the case, otherwise if I loose I will be removed from my Ad Hoc Position also.