Office 365 Exchange Online account OWA

I recently got a notification that one of my O365 Exchange Online accounts was full. I purged all Mailboxes of messages and their contents (even Deleted Items). I'm still getting the notification that the Mailbox is full. This is an Exchange Online account so NO OUTLOOK. Everything that I've done and can do must be done through the O365 Portal. How do I clean out the mailbox when there is nothing in my Inbox, Sent Items, Drafts, Junk Mail, Archive and Deleted Items? Thanks.