reCAPTCHA Validation Question

So now my question is how to make reCAPTCHA more robust. Seems I have actual humans spoofing my forms, just needing to check the reCAPTCHA box is simple enough. I have increased the complexity level of the CAPTCHA on the google admin side, which seems to have no effect, it is still a simple checkbox. Are there any options available to configure to increase the difficulty. Also how would I customize the alert message when skipping the CAPTCHA field?

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