Something to say about rengar top and bot

Here I am playing ashe with a thresh by my side. the enemy picks janna + rengo bot. The rengo got 2 kills at the beginning of the game because of their invasion, I did not die. On lane we double killed them. Back to the lane, the rengo comeback with 2 long swords and one dark seal. Im kinda new to this game so I'm not sure why. He leaps out of a warded bush and one shot me. Then he get fed and carried the game. How to prevent this from happening if your sup is anything but a soraka or nami. legit this is not balanced in low elo.