Hi and welcome to the forum @Anonymous User,
NOW TV is a fully 'online service' which offers help to its customers via Live Chat, via Email or via this forum (by forum members, along with a comprehensive range of Help Centre articles). And as such, there is no telephone number...
That being said, provided you have not viewed any content after cancellation (which the NOW TV people will thoroughly check) you should be able to get all (or a proportion) of your subscription payments returned to you by contacting a NOW TV representative via the forums 'Live Chat' facility.
The easiest way of accessing 'Live Chat' is by using a Windows or Mac computer, along with various many makes and models of mobile phones and tablets (provided their screen resolution is high enough). Here's what you need to do: -