Remove someone else's device and passkey on my Gmail account

I have many email accounts, and a hacker has locked a passkey and device on my accounts. It started out using the same name as my device, but then I renamed mine and saw it was a different device. I have tried every method through Google help to remove this device and the passkey, and nothing works. The passkeys option to remove is missing. I have put a password PIN on Gmail and changed passwords. I've logged out, removed from the account, logged in from different browsers, etc., a couple of times. I was able to use the "Find My Phone" app, and it showed different addresses. I was able to rename his device to something else so I can see it on my account. I don't know what else to do. He has opened other accounts in my name and linked them to mine, changed passwords, accessed my cloud email, social media, bank info, personal information, and who knows what else. I've canceled what I can. I'm backing my info up now. When I delete my Google accounts, he recovers them. I found out by logging back into them that they are still open. He redirected my recovery codes to those accounts, so I can't get them. He's blocked my live chats, so I can't get help. Right now, my plan of action is to back up my files, photos, and contacts. Delete all my accounts, RESET my phone, and hope this works. Will this be enough? He has all my Device Info and even my address. If I could delete the devices and passkey, would that sever the connection? I'm open to any help or advice! THANKS!