Hello,
I have installed "Integration with ReCaptcha Plugin" to prevent spam users on registration. But still spam users are registering .
I think this is not working efficiently
Having a Captcha on your website doesn't mean that you won't get spam users registered. It just mean that you'll have less of them.
For example, on our own website, we have ReCaptcha and an email validation, and we still get every week spam posts on our forum that we have to clean.
There is no 100% solution to prevent any spam. It's the same with gmail. Even though they have an amazing system to catch spam emails, there are still spam emails reaching my gmail mailbox and sometimes real emails getting flagged as spam.
There is not much you can do besides trying a different captcha system. For example, this extension is a Captcha extension and supports HikaShop:
extensions.joomla.org/extension/keycaptcha