It sounds like you might be experiencing the used space file walker bug. High Trash usage - 27 TB - no more uploads - #29 by Alexey
I was just experimenting on my node and it looks like simply renaming or deleting the used_space_per_prefix.db and restarting the node does the trick.
After the file walker has had time to complete, the used space numbers on the dashboard should update to the correct numbers.
For some reason the used space numbers don’t save to the database on shutdown or restart but they do save to the database hourly. Also you might have to fix the used_space_per_prefix.db issued each time you restart if you want the file walker to run correctly.