The Pilgrims called on the Football Association to take action following the incident, which was missed by the officials at the time but picked up by television cameras.
Kelly, who appeared to shove the ball-boy to the ground during Orient's 3-2 win, has now been handed a hefty suspension by the FA after being found guilty of violent conduct.
An FA statement read: "It was alleged he committed an act of violent conduct in the 86th minute which was not seen by the match officials but caught on video, contrary to FA Rule E3.
"The player denied both the charge and the claim; however, following an Independent Regulatory Commission hearing on Friday evening (17 February 2017), the case in respect of the charge of violent conduct was found proven.
"Furthermore, the Regulatory Commission considered the standard penalty to be insufficient and ordered he serve an additional three-match suspension, resulting in six matches in total."