@jonehar53
Is this on Wi-fi or Ethernet?
Have you done a factory reset to the router by holding the reset button for 15 seconds?
For Wi-fi you could split the bands if you haven't done so already.
https://help.nowtv.com/article/improve-broadband-speed
Failing that, I would call the broadband team and ask for full investigation of the lines all the way to the cabinet, it is possible something has become faulty on a main line.
See below link for number.
https://help.nowtv.com/article/how-to-submit-a-broadband-complaint1
FYI that I do not work for NOW, just a NOW customer trying to help