When my users create new site, they can do it, but the url

When my users create new site, they can do it, but the url ie xxx.mysite.com is not accessible. Browser reports that the page doesn't exist. I have contacted hosting support, the problem is not on their site, wildcard is set normally..so no clue. Now users can register their site, but it's not published - obvioulsly. What to do, any solutions?