When You call Samsung they will tell you to turn off your router and tv at the same time and turn them back on. After doing that you wait a while and the Netflix ESN will popup.
I just purchased a Samsung smart TV and found that the Netflix app would not work although everything else did work. After much research, chats with support, etc. what my wife found was that the Netflix ESN (electronic serial number) was blank.
To check this use the 'Menu' button on the remote and select 'Support'. From the support list, select 'Contact Samsung'. This will show the TV model number, serial number and Netflix ESN.
If the Netflix ESN is blank then you need to call Samsung support as the fix was for the support tech to remotely access the TV and reset the TV. Doing this populated the Netflix ESN and everything is now working.