Cannot Add my Emails to iPhone

Hi.

I recently bought iPhone 7Plus and managed to add my yahoo email. There was a problem where I could not get recent emails being sent so I decided to delete it and eneter it again. After I deleted it, it won’t allow me to add it. I manage to enter my email address and password then after loading, It briefly brings the sync page then it takes me back to the sign in page. I have tried adding it multiple times and the result is always the same. I have also tried adding a gmail but still no success. I am using iOS 11.4

Please help as I have contacts on my Yahoo that I need synced.