Perform the following in the Azure Console:

1. Go to Azure Active Directory
2. Go to Users and group
3. Go to Group settings
4. Set Users can create Office 365 groups to No

References:

1. https://whitepages.unlimitedviz.com/2017/01/disable-office-365-groups-2/
2. https://support.office.com/en-us/article/Control-who-can-create-Office-365-Groups-4c46c8cb-17d0-44b5-9776-005fced8e618