As you were mis-sold the TV, you have the right to take it back for a refund, and maybe to buy a Samsung or LG TV instead, which do have the NowTV app installed.
However, as per the link that @schnapps kindly gave you, it may be a lot less hassle, and maybe cheaper too, to just get a NowTV stick, £15, and plug that into the TV. And this may well have other apps on it that you were told were on the JVC, and aren’t.
If my posting answered your question, please click ‘Accept Answer’ If you liked my posting, please click ‘Thanks’. If you disagree with my posting, say so below, and I will see if I need to mend my ways 🙂