Important Emails and Folder Disappeared

I have lost certain important emails and a whole folder and I can not retrieve them.  I did not delete them (hence the *important* part). One day I just logged on and they were gone. I've looked in the search bar and nothing comes up, checked trash (and recovered trash), and NOTHING!  I even came on here and read several "solutions" to try and nothing has worked.  This is a fault of Xfinity. These are highly sensitive and important emails that just vanished and something needs to be done about this.  This has occurred on the website and on my phone.