Luis,
I think the reason you can’t call them is..
Because when they connect they get
a different IP address each time.
If cable then maybe everytime they turn on their computer they get a
different IP address.
In short your system doesn’t know their address because it keeps changing.
Their firewall program might be causing the same problem.
Just some thoughts.
I don’t have a webswitch so I might be way of base.
Good Luck,
Lost