How to eliminate old url content

Hi,
recently i changed one URL on my site, causing a great disaster.

All the content for that url (that also affects others, it’s structured example/sub-example/sub-sub-example/ and the first is the changed)
got duplicated on google, and don’t know how to fix it, because i can’t create 301 redirection because there’s no old url, it’s the same page, and can’t use rel=canonical neither i think, correct me if i am wrong.

So what should i do? May I use Webmaster tools robots an order them to ignore all old urls?

Thanks you guys.