Hacked iCloud email account: How to report and ensure safety?

I have received an email from my own iCloud account, but it is a hacker threatening and blackmailing me. I have changed my Apple account password and made sure no other devices are connected. I have made sure my personal information is all correct and nothing is seeming out of place however I don’t know how to report this or how to make sure I am safe. I am not a tech savvy person I communicate better by speaking to someone.

Please can anyone advise what I should do? I am genuinely concerned. I do not have an Apple Store near me to visit and discuss with someone. Is there a contact number to speak with somebody? If they’ve managed to email me off of my own email account, do they have all of my information? Have I done enough to prevent further harm? Any responses are greatly appreciated.

[Re-Titled by Moderator]

Original Title: Hacked email?