How to unset a session in webview

Hi guys,

In my app it just calls a webview, everything is done via the php code on the webserver.

When a user registers, the php sesisons works very well with the app. (maybe too well)
The user has an option to delete their account, if they do that the session is unset:
session_unset();
session_destroy();

But if they reopen the app, the session is still set, and they are able to get into the members area (the members page checks if session is set or not) and basically they are in the members area with no valid account.

Anyone know any other ways I can kill the session?

thanks