I need some advice

How do i play against a fed and as without having much help from my team. These three champions have really been a problem for in ranked. It really doesn't matter how many times they're killed early game they end up getting fed after getting like 2 items. I'm able to 1v1 them at times but after they hit 4 items they just burst me down in seconds even if i'm a whole item a head of them. So if anyone has any advice on what i can build or do to prevent them from getting any form of lead. I could play other champions bot lane but is the champion I'm having the best luck with recently in being able to solo carry games .