Welcome to the forum. First off make sure you've cancelled any passes you don't want as they will roll over each month until cancelled.
You can cancel your pass by going to your My Account > My Passes page http://account.nowtv.com/passes
You should see a list of any active passes you have on your account, with a cancel button next to them. Just click cancel and follow the steps all the way to the end.You should receive an email confirmation but you might want to take a screenshot of the cancelled pass as well.
If you have more than one type of pass you need to cancel each separately.
As for a refund, if you haven't already your first step should be to try talking to live chat, explaining the situation and seeing if they can do anything for you. To get there go to the following help page
I would also recommend enabling your Payment PIN in your account, this will prevent accidental or unauthorised payments in the future. If you have a NOW TV Box it's easy for people to accidentally purchase a pass. To turn your Payment PIN on, go to your My Account > Payment PIN page
Similar thing happened to me. Did the free trial & then cancelled the passes I had trialled in March this year. They have been taking about 17-18 pound off me every month since. Only just noticed it on my bank statement. Haven't used Nowtv since the trial and they will only refund me for 2 months. Ridiculous. Was told this would be "escalated" but haven't had the follow up email I was promised. I will be taking this to Consumer Rights & telling everyone I know to have nothing to do with Nowtv.
I too was ripped off by now, only had 1months trail, cancelled within the time allowed, never used the box afterwards was unpluged and put away, but for seven months now continued to charge me each month as it showed on my sttatement, and each time i got in touch to complain, £67.91 was taken by now, they said they would get back to me about this, nothing happend, every now and then they pester me with offers, i just pester them about the refund, 4 years on, still being pesterd still rattling on about the refund, but the other night i contacted now via live chat like i always do and demaned a refund as i dont have now tv, the advisvor said i should have contacted them sooner, he said i could get two months back, i said no the full amount, he said no only two months, i said no full amount, nothing came of it except now tv have wrote and told me that im happy to close my complaint, nòoooooo im not, its still ££67.91 , if your unhappy about how much they charge, contact trading standards like i did, my trading standards team say now cannot charge someone for a service they no longer have, desipite repeated attemps to alert now about the problem they continued to take money and ignored my complaint, the issue to resolve the seems to be that you cannot have now tv without a contract, its all a pack of lies, febuary 2014. I stopped watching now tv, its december 2018 im still waiting for my refund. And im going to get it, now tv have chosen the wrong guy to mess with, so if now dont pay up i just tell the everyone what they did, how ever your case is much stronger than mine i would demand total refund in your case.