Your Facebook password should be at least 12 characters long, with upper/lower case letters, numbers, and symbols. Do not reuse it anywhere else.
This is a typo or shorthand. Most text files containing passwords are named passwords.txt or password.txt. The term "passwordtxt" is likely a concatenated version used by hackers or script-kiddies searching for poorly stored credential files. index of passwordtxt facebook
After changing your password, use the "Log out of all sessions" button. This kicks the hacker out. Your Facebook password should be at least 12