Unauthorized devices using my account

An unknown Mac that I did not authorize has access to my iCloud account, and has control over all settings. The past few devices I purchased were immediately compromised and accessed remotely. When I make changes to my Apple ID and account, My actions are overridden by devices that I have no access to. How should I begin to correct this problem? its been disrupting my life for years, and my information has been used to create several synthetic identities. I cannot find employment and my credit has suffered immensely. Any advice on where to whim to regain control of my information? some accounts wont allow me to recover them because after review, I’m denied access. the only device I own is this iphone 11. Since the day I purchased it from Att, it was compromised despite creating a new phone number, Apple ID, etc. Please help!