Hi Eduardo,
Please try to comment without reCAPTCHA validation. Does it allow you to comment? If it doesn't than reCAPTCHA works fine. It seems you have other comment plugins which open doors for spams. Or maybe on some Pages the wpDiscuz is not enabled, so spam bots attacks default comment form. Make sure wpDiscuz is enabled for all your post types.
Also, I'd like to see what kind of spam you're talking about, could you please show some examples (screenshot of dashboard > comments page) and leave some URL.
If you have other captcha/reCAPTCHA plugins activated for comments please disable those.
P.S. the wpDiscuz Google reCAPTCHA is well tested and approved that it works correctly and stops all kind of comment spams. This is a solid addon which is installed and currently used on hundreds of websites.