Applying for mentor is not allowed for users with rejected mentor profile

[yellalena]

1. I create an account
2. I apply for a mentor
3. My mentor application gets rejected, I receive an email
4. But on the website, I still have "Become a mentor" button
5. Trying to send application returns "Server responded with 409", not very informative for the user

Objective:
Whether the button should not be displayed at all or the user should receive meaningful message on why they can't send a mentor request, because rejected mentor information is not displayed anywhere for the user.