Hello, if you believe that Netflix have made a mistake and over charged you, contact them directly here, and explain your problem to them.
You can look here for Netflix's help centre where they address similar problems to this.
A possibility is that you have accidentally created multiple accounts. You can check if this is the case following these steps:
Go to Netflix.com/LoginHelp and enter any email addresses you own to check if they are linked to a Netflix account. You will have to enter one email address at a time, and select Email Me after each one.
If you see an Email Sent confirmation message, sign in to that email and follow the steps in the password reset email.
Sign in to that account with your new password, then cancel the account. Remember to repeat these steps for each of your email addresses!