How do I stop automatic syncing?

I have an iPod Classic, iTunes 12.7.1.14 and macOS Sierra 10.12.4

In iTunes Preferences I have checked the 'prevent iTunes from syncing automatically' and 'Manually manage music and videos' in the device options, yet every time I connect my iPod it syncs automatically and I have to wait an age before I can disconnect it. Can anyone advise me how to stop this auto-sync?