I am sorry you have to go through this – is it possible to share with me the cpanel login and wordpress login to this site so that I can have a closer look? I will delete the theme folder and recreate the same and hence pls let me know if you have any customizations there, so that we can preserve them. The settings data won’t be lost since it resides in the database.
Also will install wordfence security plugin so that you instantly receive a notification if a file like maink.php was uploaded by modifying the wordpress folder. The plugin will notification even if there is slight modification to the theme or plugin files for any reason.
I hope you had the latest version of Invent and WordPress installed on this server.