I guess there is an issue in the Quota calculation of Free email storage quota, where it is showing 821MB/1MB instead of 821MB/1GB resulting in the quota exceeded error eventually.
The error doesn't stop here, the issue also shows in the secureserver webmail where it gives the message storage exceeded by 821000% which also is inaccurate.
I'm not sure the email will keep working normally or it will be revoking and rejecting emails due to an erronous "not enough storage" message.
Hopefully someone can or will look into it.
Were you able to get this worked out? What you're describing sounds like an account specific issue that no one here in the community is going to have direct access to review as this is a public discussion forum.
If you're still needing assistance with this error, you'll need to reach out to our live support via phone or chat so they can help investigate.