benreic parent
I also got a C2 and briefly connected it via WiFi before I had the Apple TV. After hooking up the Apple TV I turned WiFi and thought I was all set, but it keeps turning WiFi on by itself and checking for updates which is really annoying. Might do a factory reset to clear out the WiFi password.
Change your wifi password, give the new password to your TV and make sure it connects, then change the wifi password (either to another new password or to the old one) and don't give the new new password to the TV. They generally don't remember and try previous passwords.
Go into your router and block the MAC address. Even most ISP routers have an option for this, sometimes in the Parental Controls section. Much easier than changing the password or resetting the TV.
Just change the wifi password. :-)