My best guess is that Anaconda is tricking you and sets a default IP address on your network interface. If DHCP is not available NethServer defaults to 192.168.1.1
Maybe this discussion can shed some light: Set LAN IP after install
If you have SSH / Terminal access to the server you can manually configure the network interface:
db networks setprop YOURINTERFACENAME ipaddr DESIREDIPADDRESS netmask 255.255.255.0 role green
signal-event interface-update
Then you should be able to acces the admin webinterface through https://DESIREDIPADDRESS:980
The IPADRESS should be known by your VPS host.
If you do have SSH access, but no webinterface, can you check if the httpd service is running?
I am not familiar with Server4you, but I have NethServer running on a Contabo VPS.