Dear Ajit,
You have written that "6 months ago I was retained with some financial COMMITMENTS OVER EMAIL". From the sentence, it can be deduced that you had submitted your resignation and in the post-resignation negotiations this commitment was given. Probably, it was for the X% increase in the salary after the subsequent appraisal.
Now you say that all other employees were given the salary raise but not you. Therefore, it can be inferred that the commitment to you on the salary hike through email was just a ploy to buy the time. Now it appears that should you quit your employment, your employer is confident to arrange your replacement.
You wanted to highlight this discrimination and wanted to know how to do it. Against this backdrop, I recommend you not raise the matter at all but start looking for the change of job and once you get it, quit the employment. I say so because the intentions of your employer are well clear and raising the matter will not help much. What is the point in continuing with an employer who does not honour his/her commitment? Of course, getting the right kind of job is not that easy nevertheless, keep the search on. One someday, your efforts will succeed.
One more important point. By giving the salary hike to everybody except you, the employer has conveyed a signal that you are persona non grata to him. By singling you out from the salary hike, he wants you to quit the employment. If you do not quit on your own then you could be told to do so in the coming months. So search the job vigorously!
Thanks,
Dinesh Divekar