Fix security issue on website (custom script)

I have a big security issue regarding to my script.
A few weeks ago somebody steal this script and like a couple of days this guy begin to change all my database.
we are in diferent server i change the password of the cpanel and database but still not working, so i have to make backup every time that this guy change the db.
i need to fix this issue as soon as possible.
pd: the creator of the script disappear...