Permissions for Data folder on external Harddrive

So i reinstalled Nextcloud on my Pi, because i got now an external harddrive to connect. So i used:
sudo ln -s media/pi/Elementals/Nextcloud/data /var/www/nextcloud/data

and i changed the the owner inside var /www/nextcloud to www-data for the data folder there.
Still i cant install it. I tried to change the owner of /media/pi/Elementals/Nextcloud/data. But cant change it.
im using:
chown -R www-data:www-data data/
Even thos when i use:
sudo -u www-data bash
and then create a folder its owned by pi.
What i did wrong ?