Being underpaid and asking for a raise
I have been working for my company for 6 months and they just did a salary review of everyone and the people who were employed with or after me got the salary review while I heard nothing and my salary is still the same apart from the fact that I got a slight increase since I succeeded my probation (however, I was advised that I would increase by this much in my contract so it is definitely not the salary review that they did). I was very tempted to tell HR regarding this, however, I was afraid that I would sound very ungrateful so I decided not to.
However, now a new employee got recruited and he has just graduated (so he is not more experienced than I am since I have a degree and 1 year work experience in total) and I heard him say that he has been given an X amount of salary which is the same as my salary AFTER my probation (he would increase when his 6 months are over and get a higher salary than mine!). Additionally, I was asked by my manager to start doing abnormal support 24/7 and I am very angry and disappointed to say the least that I would be given more responsibility and from all the employees I was the one that was not given the salary review!
How should I handle it? I want to email HR about this but I do not know how to word this and not sound ungrateful (NB we cannot discuss how much we earn so I don't know if I should say that I heard an employee do so).
Thanks in advance!