I deleted an obsolete backup, but my Dropbox space hasn't changed. What to do next?

I too have received a warning that my storage space is almost gone.  Almost all the storage space was allocated to a useless backup against an unplugged device that I no longer have access to. 

 

The backup status showed unplugged, which it was, and told me to reattach the device, which I couldn't.  The full backup would require more than my 2GB of storage space, so it paused. After several attempts, I was able to delete the backup. However, this did not release the storage space.

 

All the suggested recipes for managing backup storage start with 'select the backup', which I cannot do. Any suggestions?

 

Thanks