Issue I got Hacked and files permissions keeps on changing

[Nehodev]

I have a WordPress website hosted on Plesk, it got hacked and when I go to the File manager to change any file inside the httpdocs I can't all of the files are set to be readable and executable only and whatever I try to change it instantly gets to be the same (readable and executable only).
my website is no longer accessible it is marked Broken how Can I fix this