Hi there! Sorry about the confusion this has caused. While you changed your username, you may have inadvertently changed your blog address as well:
Selecting “Change example.wordpress.com to match my new username and discard the old address” will change the address of your current blog. If your new user name is newusername, your blog’s address will be changed to newusername.wordpress.com
Though your blog address has changed, your content is still intact in your new blog:
If you'd like, I can help you get your old address back and transfer your contents there. Let me know how you wish to move forward. Thanks!