Anyone know who to report a debt collector for breaking the federal law. I've got one calling me at work.

I have told this agency to stop calling my workplace and have given them a good cell phone number to reach me. I was told "I can call your workplace if I want to and there's nothing you can do about it. Maybe if you get embarrassed enough, you'll pay your bill." I have a current payment arrangement worked out but the phone calls still come.