Yahoo calendar will not sync to IPhone

My Yahoo calendar has stopped syncing with my IPhone. When I click on "Calendars" at the bottom of my calendar app, it says "Verify Account Information" and when I click on that it says "Incorrect Password Your username or password is incorrect." I have deleted and reinstalled my Yahoo account multiple time so now when I try to add a calendar, there are over ten potential Yahoo accounts. I cannot delete them and cannot get my Yahoo calendar back. Any help? My Yahoo calendar is available online. My Yahoo email works on my IPhone. I have updated everything. I think I am going crazy.