@FreyaL
You don't get billed for Wi-fi, its your broadband connection that is billed. That in turn gives you both Wi-fi and Ethernet connections to the internet.
Best option for you is to call the team.
https://help.nowtv.com/get-in-touch/now-broadband-calls/managing-my-payments
NOW Broadband Members can call us 8am–8pm, 7 days a week.
03300 412485
FYI that I do not work for NOW, just a NOW customer trying to help