Hello,
The form at the bottom of your articles are in fact Comment Forms, usually built into WordPress, and are no Contact Form 7 Forms.
Contact Form 7 is a WordPress plugin to help build custom contact forms.
Comment Forms are built into WordPress and can be enabled by default on posts. They’re a way for your community to interact with your posts.
If you don’t want users to leave comments on your articles, you could disable comments entirely. There is a Disable Comments plugin you could install. The settings are under Settings -> Disable Comments.
If you want to keep comments on articles but have a ReCaptcha to prevent spam, you could install Advanced Google reCAPTCHA plugin
In short, the ReCaptcha v2 for Contact Form 7 plugin you’ve installed does not work on Comment Forms. Hopefully using the recommendations above you’re able to find a solution to your spam problem.