Very sorry for the frustration with logging in and managing your password! It may be that your new password is not being accepted due to security requirements as opposed to the listed character requirements.
Some security requirements for your password are that it cannot contain parts of your name, the company name, or parts of your email address. We have this requirement to ensure that passwords are not easy to be guessed by malicious third-parties and your account remains safe.
Let us know if following some of these recommendations allows you to set a new password for your user.