My notes icon is there but all the notes have gone

If you deleted the notes by mistake, follow the steps:

Recover recently deleted notes

1. In Notes on iCloud.com, select Recently Deleted in the folder list on the left. If you don't see Recently Deleted, you don't have any notes in that folder, and there's nothing to be recovered. ... 
2. Select a note, then click Recover in the toolbar. The note moves to the Notes folder.

Make sure that iCloud Backup is turned on in Settings > [your name] > iCloud > iCloud Backup. Then see if the notes is enabled. now try again and see.. Good luck!