Depends on which applications you selected when creating database for Odoo online, there is limit of applications which are free and rest are covered on 15 days trail part of odoo online once days completed the database is locked and is accessible to some modules. If you have technical knowledge regarding odoo development. I will suggest to examine access logs from My databases | Click on gear sign and click on view access logs. I would suggest you should provide more information or contact support for it.