-How can I determine who's network this is? And if I can how can I contact it. I have it's mac address it's not used by me or my family.My neighbors live too far away(50+ meters) so it shouldn't be theirs either.
There isn't a real way. Aside from investigating the side of every device to see if the MAC matches, all I can recommend is that you signal check and go where it's strongest.
Is there a simple command(windows) to see who's connected to the same network as I am?
No simple command, but NMap is a good way of plotting what devices are connected to your network. There is a windows port you can use and lots of good guides on the internet about how to use it.
Currently my network is protected by password and white list, how can I defend it better?
Use the highest level of encreption possible. Wep is totally useless, WPA is next to creacked, WPA2 is pretty good. Keep in mind that the security of your network depend on the complexity of the password itself. Correct horse battery staple rules are in effect.
Some general observations -->
Some devices (like wireless printers) use access points as a way to quick setup. It's not necessarily a rogue network.
Also, because all devices share the same wireless airspace, even those that are not connected to your network can interfere with them. So, imagine that someone is using the same channel as your router, your router will know to only transmit when the other AP is not. Effectively they will take turns, even though neither has access to the other.
I think you might be a bit too worried about this, but NMap is a really good tool to learn how to use, so if you want to be extra sure I'd start there.