This is working solution for disabling Windows auto Update. Tested on 2008 -> 2016 operating systems:
Disable auto update check:
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\WindowsUpdate\AU
Key: NoAutoUpdate 1 = Disable Automatic Updates. (Reg_DWORD)
Disable manual download:
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows\WindowsUpdate
Key : DisableWindowsUpdateAccess 1 = Disables access to Windows Update.(Reg_DWORD)
Details: https://github.com/vFense/vFenseAgent-win/wiki/Registry-keys-for-configuring-Automatic-Updates-&-WSUS