Complaint letter on salary increase

please can someone help me out in writing a formal letter of complaint to my employer on my salary increase. i have been working with the firm for over 2 years, about a year ago an increament was made was i was sidelined and after quering the human resources dept i was informed that it was due to my immediate boss recommendation now another period for increase had come with the hope that i would be on the same level with my other colleagues only for me to find out the increment still made me to be at the bottom of the ladder.