You can PM any forum moderator by going to their profile page (click on their name) and selecting the 'Message' option. No guarantee that they will reply, of course
Note however that it is standard practice for the Mod team to close threads talking about moderator actions, so this one may be closed as well.
If you are having difficulty with your access code, please contact customer support as recommended here. Lacking access to your account is a hindrance when you need general customer assistance.
If you otherwise need clarification on why a thread was closed, please contact the moderator who closed the thread for further information. Keep in mind however when locking an thread we will usually leave a comment explaining the reason behind the closing of the thread. You may want to check the thread's comments. Forum issues are not handled by customer support but with the moderators present on the forums.