Hi and welcome to the forum @DWC1,
First things first. Can you please confirm the model of your NOW TV playback device?
Is it the NOW TV 'white' (Roku LT) box? Which looks like this: -
Is it the NOW TV 'black' (4200SK - Roku 3) box? Which looks like this: -
Is it the NOW TV 'smart' (4500SK - NOW TV) box? Which looks like this: -
I am guessing you have tried replacing the batteries on the remote controller.
Also, do you own either a smart phone or tablet, if so have you tried the free Roku remote control App from your device App Store to see if that works on your smart box.
If the Roku remote control app works on the box then maybe you can go into the box menu settings to undertake a factory reset.
Please by aware that once you factory reset the box you will need a fully functional nowtv remote controller to setup the box again from scratch (the Roku app will not work for initial setting up of the NowTV box).
If the smart box is in the warranty period and the Roku remote App works, i would try a factory reset on the box because you got nothing to lose and if you can not setup the box again you can always get a replacement.
Should the box be out of warranty, then you may have to stick with the Roku App or take a gamble on a replacement remote controller (unless you have either an older white or black nowtv remote controller spare in the house).
There is no guarantee that a replacement remote would solve the issue, there could be a problem with the IR receiver on the box or some other inherent fault.