Really Simple CAPTCHA is now excluded from Contact Form 7 by default.
It is recommended to use reCAPTCHA now, but if you want, you can still use Really Simple CAPTCHA, but it must be “turned on” first.
Folow this link for more info and how to:
https://contactform7.com/2015/09/17/contact-form-7-43/
Hope this helps.
