I have been experiencing spamming in my website for a long time, following are two things i want to stop -

1.stopping fake/bad user registration 
2.stopping posting bad topics in my kunena forum 

I have captcha and registration confirmation email enabled when new users registers in my website, but still many fake users are registering, most of their emails ending in mail.ru and yandex.com. For this in my gmail account i am getting too many delivery incomplete and registration pending approval emails because most of those emails not exists and have many restrictions so that their registration is not being complete, i want to stop all these emails too.

I have done many researches about how to stop them, i got users' ip addresses from k2 user list and added those ips in restricted list from my server control panel but all those ips different and how long i can do that?, I found recommendations from experts to use EasyCalcCheck extension but it's not free and i can't use it after installation, also i checked akeeba admin tools extension but did not see any settings for this yet.

One thing spinning in my mind if they were using bot when registering then could they pass captcha input restriction? so some measurements like putting hidden inputs and asking to answer questions before registering may not work because they are freaky minded human registering themselves not any bot or am i wrong?

So i need very strong suggestions about what to do to stop fake/bad user registrations(6/7 registration attempts on avg each day) and posting bad topics in kunena forum(on topic posting, i set captcha challenge for users in kunena settings and tried other available settings). FYI i am using CB for registration.

Update: I think this question is not exact duplicate of any other questions(like this one), reasons are that i addressed two concerns that is not only to deal with fake/bad users but also to deal with posting bad topics in my kunena forum.Also there are differences between what I and other authors wanting to get by these questions.

There are not many posts of this kind and it does not match exactly with any questions, so just keep it so that community gets benefitted from it.