Also, i advise you tu use the new Google Re-Captcha :
First, click on Get reCAPTACHA (on top right):
https://www.google.com/recaptcha/intro/index.html
And add your domain with and without subdomain :
ex : https://www.web-premiere.fr and web-premiere.fr
After, stay on this page and install the plugin on your WordPress :
WP reCaptcha Integration : https://www.ads-software.com/plugins/wp-recaptcha/
Install it and copy and paste your site key and secret key.
At the end, go on your Contact Form (with contact form 7) and add : reCAPTCHA.
And that’s it !
My website for people interested in my work : https://www.web-premiere.fr/
Cheers.