Unfortunately, there is no captcha that could provide 100% spam protection. Real people (and spammers) can get through captcha easily.
Here is a list of simple recommendations to stop spam on your Wordpress website:
1) Make sure that the reCaptcha plugin is installed, activated, updated to the latest version, and integrated into your form(-s).
2) Try to submit your form(-s) without captcha (or use the wrong answer to make sure that reCaptcha is working correctly).
3) Install and activate Limit Attempts plugin to get additional anti-spam protection and low-down bots registration rate. Learn more - Limit Attempts by BestWebSoft plugin.
This article related to reCaptcha by BestWebSoft plugin
Additional resources: reCaptcha - User Guide
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