You’re using the Illdy theme, from what I see, which should be fully responsive – https://colorlib.com/wp/themes/illdy/.

I took a look at your website, and it is responsive, except for some parts where there are some fixed widths. Perhaps you’ve set those fixed widths or selected an option that prevents them to scale properly.

The problem only appears where you added images (images shouldn’t have fixed widths in order for them to be responsive) and that Custom Facebook Feed plugin.

I believe it’s just a setup issue, and I recommend checking the theme options again, pages, or if you use a page builder…

I don’t think there’s something wrong with the theme.