WordPress Category slug

I changed the category slug,everything was working correctly, but after some time I observed the old slug remains also.

For example:

old page: /cryptography-computer-security/sample.php
new page /cryptography/sample.php

The problem is that both links are working and have the same content. So I have duplicate content.I tried to use Rewrite and Redirect in .htacces (apache) but is not working(doesn’t rewrite,redirect the url).

I searched in database , table wp_terms and the old slug wasn’t there.So I don’t know how to resolve the problem, also I am searching for and advanced wordpress database tutorial.