Various Authentication Methods used by ISP's

I would like to know the various ways by which ISP's verify the various devices connected to their network.
I live in a student apartment building with only 1 ISP for the whole building. This ISP doesn't like the idea of clients sharing or distributing the same internet line.
I purchased a wireless router in order to obtain wireless connectivity in & around my room, especially because i like using wifi on my mobile phone.
My ISP then introduced MAC address authentication in order to limit the widespread use of routers, but i later figured that out and simply had to clone my pc's MAC address so that my router could obtain connectivity.
But it's been about a month now since my router has lost connectivity. The only way by which i get internet is by directly connecting my pc and entering the appropriate static ip address. All my friends who also use routers in their rooms have also lost internet connection through router.
I've been trying to figure out exactly which method he is presently using to authenticate the various devices connected to his network, so that i could use my router to also emulate my pc.
All ideas are welcome!!!

Give up, you won't be able to get around it. They're packet sniffing. Any web data that comes out has additional info embedded. They see the packet contains info for multiple devices and block that way.

You plug in your computer and it doesn't have that header information in it and it is allowed.