Hi @hussainyousaf,
We were experiencing the same issue a while back, in our case by turning on the registration validation was already suffice. Find this line in config.inc.php:
We did it manually by selecting multiple spam users via phpmyadmin, you can find the user database in the users table.
Via phpmyadmin you can also do the MySql query described in previous thread, specifically this one. As we are not experienced in running query, we cannot guide you.