1. If all the similarly circumstanced employees got regularisation and got confirmation except you then you have good case challenging the non conformation .
2. In that event you can take plea of bias and mala fide intention and hence challenge their action by filing the writ petition in high court.
3.Since during your service period there was no adverse report on your conduct I find no reason of failure of your case if you fight for justice in high court in its writ jurisdiction.
Good luck.