Providing everything up to date, in theory the LG C7 will do a form of Atmos over Arc, it will DD+Atmos. Recheck the sound settings on the Tv to see that it is using the right mode, if the ARC is working for everything else. As mention before you need the UHD subscription and correct settings on the Netflix app, the title should indicate Dolby Vision/Atmos. The alternative would be to try streaming externally via a shield, Roku, Apple TV or Xbox one.