I shouldn't be banned from playing for 30 minutes from not picking a champion to ban.

It starts off with me in a champ select i accept then the picks start, i choose tahm kench and we start picking bans. after that we pick champions but the person after me does not pick so im back in Que and i get the same team against the same team and they ban tahm so i want to leave cause its a normal and i dint get my champion (i know i should've just played in blind, but i just woke up and didn't realize) anyways i get six minutes for leaving no warning no nothing. i get it whatever, so later in the day im playing with friends and we have to wait 20 min. we wait and we get in que, then the bans come and im second i dont know who to choose and at the last second i pick and click ban even made the effect of clicking. but instead of getting the ban i get 30 min ban for not choosing when i did. Even so i should not be given that punishment.