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I assume you have unplugged the home hub, and are connecting this router to exactly the same port on the ONT?
If the N66U is now the only router connected to the ONT you might want to try disabling the VLAN ID. See if that helps.
Disabling the VLAN did the trick, and I'm now connected.
Thanks to all for their help; this probably isn't the most interesting thread you've ever commented on, but you've helped me out.