Hello 
I think the reason you no longer have the option to log in via Office 365 is possibly because the person who is in charge of your Moodle has not set it up again or maybe prevented it from being accessible. It is not a standard feature of Moodle; it is an add-on feature which presumably was added to your Moodle site at some point in the past. Are you able to get in touch with your administrator to resolve this? Or perhaps the company who hosts your Moodle? If you are the administrator then perhaps you can give some more details and people on here can try to help further.