If you set the oAuth callback URL explicitly in your code by doing something like the following
$OAUTH_CALLBACK='[Callback_URL]';
where [Callback_URL] is your callback URL, then either do not explicitly assign one as oAuth 2.0 allows for this I believe, or just fix it to the right URL. I was having the exactly the same problem. Even though you changed your callback URL on Twitter, if you’re explicitly assigning a callback URL in your code, it’ll override whatever URL you set on Twitter.