Hello, my name is Agnes. I am facing the same problem on my iPhone 5. I already follows the instruction on apple support and repeat to delete my yahoo account on my iphone and add it again after changing my yahoomail password on web mail log on (almost 10 times) . I also tried to reset my apple ID password, but nothing change. I still can not add a new yahoomail to my iPhone.
Does anybody know what should i do. I really need to set up my yahoomail on my iPhone.