Leaverbuster for being afk for 3:55

I played a game of Twisted Treeline. At 20minute mark, the game was already lost. When a teamfight broke out in front of our inhibitor turret, and 2 of us died while no1 died on the enemy team i left the game. The game was done so i didn't want to reconect. I dced at 29:28 and the game ended at 33:23. After the game i got leaverbuster. I don't see a point of getting a leaverbuster for being away for 3:55 while playing a gamemode that is irrelevant in a game that has been lost for 10 minutes already. I don't know if this is the place where i should ask for help, or if getting your leaverbuster removed is even possible, but i think it's really unfair.
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