I definitely agree that HR is not your friend and not there to help you. Once they contact you about a complaint, your first move should be to get an employment lawyer. That lawyer will help you document everything and respond to situations (especially in the case where coworker contacts you again). You will still be terminated by the company, but getting the lawyer involved early will get you a severance package instead of terminated for cause.
I definitely agree that HR is not your friend and not there to help you. Once they contact you about a complaint, your first move should be to get an employment lawyer. That lawyer will help you document everything and respond to situations (especially in the case where coworker contacts you again). You will still be terminated by the company, but getting the lawyer involved early will get you a severance package instead of terminated for cause.