Cannot change new mail notification sound
I have an iphone X running IOS 11.2.6. I use both yahoo and gmail. For Yahoo mail, my new mail notification sound is stuck on Tri-tone. I have tried to change the sound by going to "Sounds & Haptics" - "New Mail" and selecting a different alert tone and still I get the Tri-tone notification. I went to "Notifications" - "Mail" -"Sounds" and selected another alert tone. Still get the Tri-tone when new mail arrives. If I go to "Settings" - "Yahoo Mail", the only option I have is to turn the notification sound on or off. Gmail has a similar issue. The sound notification is different but I see no where to change the Gmail notification sound.