First of all, I'm not sure if this is the correct place to ask this or not. If it isn't, I apologize, please direct me to the appropriate place.
First off, let me explain the situation as best I can.
I built a website for a client, www.example.ca. I take care of hosting and domain registration for them through godaddy, just so that they do not have to worry about it. I just noticed now, that if I go to www.example.net, a copy of my site comes up. It is an exact copy, and when I navigate around the website, the url in the address bar does not change to www.example.ca, it stays at www.example.net. So it's not just a redirect. This copy site also updates instantly when I update the original site. Any change I make to my .ca website is reflected on the .net site instantly. I've looked on websites that allow you to see where a website is hosted, and the .net website is apparently hosted at a different place than my site. I do not own this .net domain name. This domain name is registered to our local phonebook company.
I've been told that this is probably just a 301 redirect, but that doesn't seem right based on what I've read about it. Mind you, I'm no expert. I've also looked on websites that apparently tell you whether a domain is redirected or not, and they say that this .net domain name is not redirecting.
So now to my question, how is this possible? How did they duplicate my site, and get it to reflect any changes I make?
I hope this makes sense. Thank you in advance for any help.