HR is legal for the company. You need to take steps in your own hand. Not illegal, mind you. But you need to protect yourself.
This, a thousand times this!
In my last job, we had a media license that was set to expire after some months. My employer, thinking I was a fool, told me that we could just keep using it for a few months after the expiry and when we got caught we would just call it an "accounting error."
All along, the plan was to hold me responsible and fire me when we got caught. It's not the first time he's pulled that, so I wrote it down. He's the sort to take credit for your ideas, but blame you for his failures.
Because of him, I never trust someone who has skin in the game. They'll sell me out in a cold second ("nothing personal, it's just business.") if it'll help their bottom line or career prospects.
In short: get everything in writing, take photos of the computer clock and calender when you finish after working overtime, write down the details of any meetings or discussions. If you're in a place where health and safety issues aren't ever dealt with then photograph everything, with as much dating evidence as you can (front page of the day's paper, perhaps). Don't attend disciplinary meetings alone, have a lawyer with you.
Most importantly, know your rights and assert them. All the time. Don't let something slide just once, because "You worked one hour overtime last week, so it's now part of your job..."
Don't trust them.