A list I delete keeps reappearing after sync

Another device still has the list and is pushing it back up. Delete the list on all devices, then sync. If the list still reappears after deleting it from every device, it may also exist on the sync service itself (iCloud CalDAV, another CalDAV server, Toodledo, or Todoist), delete it from that service's web interface as well. If you sync with Apple Reminders, delete the corresponding list in the Reminders app.