What Now broadband have you got, how slow is slow exactly , and what did Now promise you?
Even I am having intermittent issues. It not only slows down, but it completely disappears sometimes too. And no communication from NOW of any update or work Also, the times when I have issues, their customer support center is closed. So cannot even call anyone for help. Very poor customer service.
Have you reported your problems to Now?
Do you know if the problems are just over Wi-Fi, have you tried using a wired connection?