Hi @JankyLV,
Sorry about the troubles you are having. These types of things can be extremely painful and time consuming. First things first, you really need to find out where the breach in your site is. This could be though a plugin or a theme or even user access. It could be WP core but trust me when I say that it is very secure but anything is possible.
The most common way a site is hacked is through a plugin or theme. The next would be the server you are on. Some shared servers allow for cross site hacking from within the server.
WordPress community has a guide for approaching a hacked WP install which can be found at https://codex.wordpress.org/FAQ_My_site_was_hacked .
I would run the following plugin to see if it comes up with anything as well.
https://wordpress.org/plugins/sucuri-scanner/