ReadyNAS 214 Deleted files not freeing disk space

I have a ReadyNAS 214 - with 4 x 2TB drives installed.

Firmware is latest at this time of writing (6.10.5 Hotfix 1).

I am running extremely low on free space and so deleted many folders of video files.  Should have freed up a ton of space.

But the free space does not change.

I have been looking through this site and also on google, and have tried various answers and suggestions, to no effect.

Please note that I have ZERO snapshots and never have.

I have looked for hidden recycle folders without luck.

I have run a Balance and also a Defrag.

I have restarted the device.

Still sitting at 2GB free - without any ideas left of what to try.

Would love it if someone could please assist!

Much thanks,

Chris