I tried without specifying any group section.
This way it worked, and all my LDAP users got assigned Contact Group. Very good.
I don’t know if our LDAP is weirdly created or what, because if I do ldapsearch to my user from server, I don’t get any group information of my user.
Anyway, I got now what I wanted, maybe I will try to work with specifying the group.
Thanks for suggestions.