@Anonymous User
Welcome to the forum.
Yep, I know that well, I usd to have an Echostar freesat box and have suffered the problem! I could even get the NOW TV remote to change channels on the Echostar as well!
Unfortunately there never turned out to be a satisfactory solution from Echostar (and as far as I know they've stopped supporting it now). If you are lucky you might be able to position the NOW TV box far enough away that the Echostar doesn't pick up the NOW TV box remote's IR commands but in most situations this is unlikely, so you are left with remembering to pair up the Echostar with its remote each time you use it (it only takes a couple of seconds, if you don't know already point the Echostar remote at the unit and hold down the OK and adjacent RIGHT arrow buttons together until the LED on the remote flashes twice).
The other solution if you have an iPhone/iPad/iPod Touch or Android phone/tablet is to download the official Roku app from the relevant App Store (there's a few unofficial ones, go for the official purple icon one from Roku Inc). This will then allow your tablet/phone to be used as a remote for your NOW TV box and because it communicates over wifi it won't knock the pairing with your Echostar out.
It's driving me mad. I have a tv box I can't use.