@Anonymous User Welcome to the community. There's a few things that can cause this, although just changing your router wireless channel shouldn't cause any of these. If you've installed a new router, check it doesn't have a built-in VPN that's enabled. Similarly check you aren't using a separate VPN or have made any other changes that make it look as if you're not in the UK (for instance changing proxy server settings, using a service to access Netflix US etc - if you have older children in the house check they haven't set anything up without you knowing).
It could also be a rogue IP you've been allocated - try powering down your router and leave it unplugged for at least 15 mins. Then power back up and see if it works.
If it doesn't then I'd suggest contacting both NOW TV and your broadband provider to get both to investigate from their end. You can send the NOW TV Team a message or get to live chat from the Contact Us page
https://help.nowtv.com/get-in-touch
(expand the Anything Else section at the bottom for options)
