Strange file behavior

Hello,
I have observed an unusual activity on the domain name
I observed two files atom.php and index.php keeps recreating themselves after I have deleted them either directly from cpanel or using ftp.
The website loads and immediately after loading, redirects to other websites. I am able to access the admin dashboard of the website but all links at the admin area take me to an error 403 page

The page I need help with: [log in to see the link]