My internet is down since day 1. Phone customer service claims that line is up, which is not true. When I log into Now portal and navigate to the technical checks, the report says that line is up and shows devices connected to broadband that are not mine.
All we can suggest to you is to keep calling broadband support.
I am guessing you have tried pressing in the small reset button on the back of the NOW Router for around 15 seconds.
Sounds like BT Openreach have crossed the line during setup with either another NOW or Sky Broadband customer, either at the street cabinet or at the exchange, where i have seen this reported in the past.
Get back on the phone to the NOW Broadband Team and question the devices showing under Technical Checks and ask for an Engineer to come out and investigate it and also sort out the internet.