To rescue your hacked website follow these steps:

1. Contact your host and diagnose the problem.
2. Properly check your user accounts and figure out whether there was a new user created. If it was, delete it. Change all the passwords.
3. Take your website offline for some time to prevent new attacks and save your visitors from a malware alert.

It is better to let the team of DevOps professionals to determine how your website was hacked. They will clean your server, remove anything that was added by the hacker, then restore your latest backup and upload clean files.