My cloned event has last year´s attendees

The registrations/attendee list is not something that is copied over when you clone an event. Since you are seeing attendees listed, it is likely that just the dates of the existing event were changed and there is not a new copy of the event. 

Try cloning the event again and follow these tips: 

• Before you start the cloning process, add the word ¨Old" to the beginning of the event name (on the Basic Settings page). This will help you keep the existing event and the new event straight. 
• Start the cloning process and when you get to the second screen (it has the same basic event settings as the first screen) be sure to type in the new name/dates. That is really the trick.