Please post the output of:
ls -la /etc/httpd/conf/sites-enabled/
I am able to get to the default index page for my website if I use "http://mydomain.com/mydomain.com/web/"
This is a bit weird as you can not access a site like this when the apache config files from ispconfig are included into the apache configuration as this access is blocked then. But according to the aapceh file that you posted, files from sites-enabled folder are included: