Office 365 Install

Firstrstv  where did you migrate from? Google or similar, or was you a free outlook.com,  generally if you sign up to microsodt 354 as a work account or tenant you initially start stil an onmicrosoft.com username which you wouks have beem guided though selecting a tenant name which prefixes that sub domain i just mentiined, so perhaps search for that onmicrosoft.com to find any clues, nb if you signed up for a free or family edition of office 365 those would of asked you to setup an outlook.com etc,  So try to find out what edition 354 you purchased, that should also have detailsnon like wwhat was used to sign up as a user but failing thay order nums etc to contact microsoft support as they can help if you have thay invoice email?