And please excuse me for asking, but are you sure the phone is working over WiFi to Now when your VPN works, and not accessing your mobile provider?
As it would be fairly unusual for Nord VPN to work over Now Broadband from your phone, and yet not from your PC, and for that to be Now Broadband’s fault, rather than an issue with your PC.
Can you try turning your phone into a mobile hotspot, with whoever provides your 3/4/5G service, and seeing if your PC/Nord VPN connection works over that?
Set a Payment PIN on your account so that no-one but you can buy memberships on it. Check your bank accounts monthly for any other unexpected payments to Now. That way you can at least nip them in the bud, while you and Now figure out whose fault they are.