no ranked for me gg (client)

i was in a ranked match and it became my turn to select a champ. i was going to go adc so when i went to select my favorite adc, jinx :), the timer started to count down like normal. i like to wait untill roughly 10 seconds left to pic so the enemy time has less time to think of counter picks but when the time reached 10 seconds i was kicked out of the match and a notification poped up and said i failed to select a champ even though i had 10 seconds to select. then i heard the timer count down noises but i counldnt do anything because i was in the home screen of league then the timer stoped an the same notification poped up again. when i went to go try to play another game it said i was banned for leaving to many games even though this was the first game i have left in months. so now im banned and this was a ranked match. pls help.