Unwanted popup ads on my WP theme

Hello, guys,
I’ve searched a lot of topics but none of them was helpful for me.
The thing is – I bought hosting and domain, installed clean wordpress and added “Cleanstart” theme. Unfortunately, I downloaded it from some website for free so I guess that’s why I get this problem. The theme works fine but I get unwanted popup ads with all my browsers.
I tried “Twenty” themes and there’s no such a problem with ads. It comes only with this theme.
I tried to disable all plugins but some of them cannot be disabled (“Plethora Themes Framework” and “WPBakery Visual Composer”).
I believe there is some malware in my theme but is it possible somehow to fix it? Or the only way to fix it would be to buy theme? (I really can’t afford that ?? )

There is my site: https://www.prolingus.lt

Thank you all.