Assuming you've done the standard reboot of the router, give the team a call. Number found in the link below.
Mine worked from 8 am. Was worried as I left SKY to join NOW. Saved me a lot of money but I do want and expect the same kind of service. I am finding the range not as good as it was with SKY though. I can’t get a signal if I’m too far down my garden, whereas I could with SKY,
To increase your Wi-fi signal your best option will be to purchase a Wi-fi extender from Amazon. Hate to say NOW will only supply the router.
Take a look at the section for splitting the Wi-Fi bands on the below link.