Hi Kowhai,
When you said “transferred my domain to office 365”, do you mean that you’ve added your own domain in Office 365?
If this is the case, Office 365 won’t send you info about FTP username and password. Please note that after you’ve added your domain in Office 365, the only change is that the DNS records will be direct to Office 365, so that you can use your own domain with the services in Office 365. FTP, however is more related to a web host instead of a domain.
For more details, please refer to the links below:
For E Plan(Office 365 for Enterprises subscription), please refer to: Add your domain to Office 365.
For P Plan(Office 365 for Professional and Small Business subscription), please refer to: Add a new domain to Office 365.