Follow this link:-
https://help.nowtv.com/gb/get-in-touch/
and work through the options until you reach the deeper options that let you either have a Live Chat with a NowTV support representative, or raise an email covering your issue, whichever means of contact you prefer.
NowTV will then be able to explain where you, or possibly they, went wrong, and more importantly no doubt, to establish your offer for the balance of £49.00
Please note that I am just a customer like you, and my advice may well be worth no more than exactly what you paid for it.