Hijack of the wordpress site

Hi!

The page that I have created has been hacked. The page was ready about month ago and it has been hijacked already. How I know why it has happened?

Chinese firms has changed the whole content. I has been now got back, but how I can avoid this thing to happen in the future?

I have plugins WPBakery Visual Composer and Silder revolution. Can it be those?

Or if you can not help, do I need to contact the creators of the plug-ins?

This is the first time when it happens to me. I appreciate the help a lot!

Best regards
Anni