my droplet hacked !! need tips

I know may there some bugs or exploite in scripts that running in droplet allow hacker to join and play. but i think my droplet need more secuirty, so I tried to secure droplet (running php and apache & link with pagespeed of google) by common methods :

install mod_security install ufw save mode (now active) active user_dir disable functions php disable ssh for root and port changed.

But hackers (Script kiddie) come again and hacked droplet, they just change template for index page, but other page you can browse well.

please share your tips :

1- service for security. 2- methods for security that restriction hacker (nobody) from change file or execute command or play with php.ini to allow safe mode …etc 3- great tool can view logs for hacker from where come.

I’m interest for paid service that help me for security and save my time.

Thank you