Please remember that Frequence Plus disappeared years ago; it is now Flying Blue.
Do not know where you are based and what is your status with FB. But have you tried calling FB in France? they are often helpful. My experience is that you sometimes get a junior person who is not well experienced with the complex procedures; so I call again to get another more-experienced agent.
That being said, RTW is not an attractive option to spend miles and very difcult to book.