Hey kextra1, i just noticed u were logged into my VPN, ill shell into your dedicated server and take a looksie of that and ur ispconfig.
FYI for falko, yes repquota -avug shows the correct value for the web which im assuming is 15gigs set by kextra1, but for the actual ispconfig user which is the admin for that web it shows a quota of 10mb.
kextra1, I dont want to change any of your configuration without permission however here may be something.
Have you checked /etc/quotagrpadmins to make sure the user and group are set to root root?
I dunno, im not to smart with quota systems, falko would be the better advisor than me.
I hope this helps!