Help on storage space

could anybody throw some light on this? the system still has 2.6Tb available, a user (unlimited quota) who used only 160 GB was told that he reaching the limit.

Thanks in advance.

Deleted files go to trash for a period of time before actually getting deleted. It’s possible the user has deleted lots of files, but the trash is taking up lots of space. See if this helps.
https://docs.nextcloud.com/server/13.0.0/user_manual/files/deleted_file_management.html

If you have shell access you can use the command “ncdu” after install ubuntu package “ncdu” (sudo apt-get install ncdu) Wikipedia ncdu

Then change in “ncdu” to the nextcloud data dir and search the biggest dirs.