Well not to hard for me to prove what you're saying isn't true. Every version you have released is available for download and in version 3.0 you added a file called functions.php that hits your website and locks the plugin if a registration key hasn't been entered in the database. I checked the plugin page and the readme.txt but still there is no mention of a registration fee. The name changed in version 3.0.11 from Expire Password to Passexpire. Like I said just look at your own code and you can see what I mean. but I guess you dont need to look at your own code. You wrote it so you already know what you're saying isnt true. You released a free plugin so that people would start using it and then hijacked them by locking the plugin and requiring a payment for software you released free under the GPL. Sounds to me like you broke the GPL and your plugin should be removed from this site.
To better prove my point that what you are doing is wrong let me take a snippet from your own code.
" This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License, version 2, as published by the Free Software Foundation."
Next let me take a snippet from the GNU liscense FAQ.
"Using the GNU GPL will require that all the released improved versions be free software. This means you can avoid the risk of having to compete with a proprietary modified version of your own work. However, in some special situations it can be better to use a more permissive license. "
So you still going to stick to your story that you didn't require payment in a later version after releasing software free under the GNU GPL?