I have a website that write URLs like this:

mypage.com/post/3453/post-title-name-person

In fact, what is important is the post and ID part (3453). The title I just add for SEO.

I changed some title names recently, but people can still using the old URL to access, because I just get the ID to open the page, so:

mypage.com/post/3453/post-title-name-person

mypage.com/post/3453/name-person
...

Will open the same page.

Is it wrong? Google webmaster tools tells me that I have 8765 duplications pages. So, to try to solve this I am redirecting old title to post/id/current-title but it seems that Google doesn't understand this redirecting and still give me duplications.

Should i redirect to not found if title doesn't match with the actual data base? (But this can be a problem because links that people shared won't open) Or what?