First choose 'NOW TV account & payments', then 'I have a query about my bill or payment date'.
Then there will be a get in touch drop down, which you would select 'broadband' or 'TV' for the live chat.
When I had broadband with Now TV, the number I used was 03300412460. Although not sure if it is still the same.
If it was TV you signed up for be aware there is no contact number.
FYI that I do not work for NOW, just a NOW customer trying to help