When you create an Office 365 account or free trial you will be prompted to enter the default domain name for your account. Be very careful here because the Microsoft system may automatically generate and add additional characters to the domain name without you noticing until it is too late.
I was working for a nonprofit in 2013 that was interested in testing Office 365. We setup an account as a trial then shortly thereafter Microsoft released Office 365 E1 free for nonprofits. I was tasked with setting up the real account for testing. Although I signed up for both accounts with the same user name and email, the new account was actually viewed as a different account by the system because setup interface had changed with the new offer. So I setup the account without noticing the system had automatically assigned an “i” at the end of the domain name which was easy to miss as the last letter in the domain name was an “l”. I totally missed the third character “llI” – lame.
Although it hadn’t really been released to users we had to completely disable our entire tenant and wait for several days until all traces left the servers before applying for the account with the correct name. That was booty.