What to do if you receive counterfeit money?

I'm a frequent shopper at a major retail store, where I cash my check every payday. I happened to receive a counterfeit bill but did not know until I went to spend it at the register. The cashier said it appeared to look faded and she ran it off to someone, who was gone for several minutes. The guy then returned (unidentified and in regular street clothes), with several people, pulling my $50 bill from his pocket asking if it was mine b/c it was fake. I replied I did not know b/c the bill was out of my site and came from his pocket so not in site of cameras to prove HE didn't do anything. He then demanded I come with him and he needed my ID to "know who he was dealing with" he said. I refused both, and explained I got that money from that exact same store when I cashed my check. I have no way to prove it he said, as I could have had other money in my purse and swapped it. I know for a fact it came from that store, as it's the only place I cash my check and really the only place I shop. There were 5-6+ ociates circled around me, so I spoke with several people at the time, as they kept calling someone else over b/c they didn't know what to do. They claimed there was no way Brinks could have given them fake money. And apparently it's not possible for other people to have given the fake money before I cashed my check and it was then given to me?? The manager on duty, gave me the fake bill back, and I paid another way and went on with my day. I have emailed corporate with no response. I later called that manager and he said I was basically out of luck and he refused to do anything. He told me to take the money to the bank and hope they swap it for me? Sounds like a dumb idea to me. What do I do in this situation? Am I out that money, do I report it, etc? I don't want the same thing to happen to someone else and them end up behind bars or something. Thanks for any help!