Leave buster for no reason.

So yesterday i was playing League like i normally do, i had to do something and i left the game for around 5 to 8 mins, i never left i AFK on fountain and i came back and I kept playing, so game was over and i got the message that i have a promotion(leave buster) of 10 minutes for 5 games and i never left the game that long to get a leave buster. Please fix that problem. I'm not expecting to get anything i just wanted to let you guys know the problem I had and see if it can be fixed. (You can give me anything though)

Hope you guys respond. -ImFerreus