iCloud hacked, macbook locked ransomware

Hello, I have a MacBook Pro mid-2014. 2 Months ago, someone got into my iCloud account which didn't have two-factor authentication enabled. They locked my MacBook Pro and attempted to lock my iPhone. That never happened to me and I thought it was going to be as easy as recovering my iCloud account and disabling the lost mode but it turns out that I can not disable the lost mode even though I recovered my iCloud account that locked it and I have the MacBook. When I try to boot up the computer I must enter a 6-digit passcode that has been set when my iCloud got compromised. The hacker who did this left a message saying: “write to email: help.apple.us@gmail.com” after contacting that email it responds asking for 50$ in bitcoins. I went to my local apple store and they told me that I can’t unlock it because I don’t have the original receipt. I tried contacting the person who sold it to me 3 years ago but they are unreachable. I had multiple calls with apple care but they seem to be stuck on a piece of paper. Is there anything I can do to prove that I am the owner of my MacBook? I am desperate at this point I can’t believe that I can’t unlock my own MacBook and that apple only cares about the receipt. I understand the concern about the security but it doesn’t make sense in this case because they know that my iCloud got compromised they sent me an email about an unusual login 2 minutes before my password gets changed and my devices get locked and clearly this isn’t a message from the previous owner because when you google the email that’s been left in the message it’s a ransom email that’s used against multiple other users in different countries. It’s really messed up that a security feature that’s supposed to protect me is used against me and apple doesn’t help me with this issue.