If it is national chain, go to corporate. First of all this is illegal in a lot of States. They have shown this on some local tv stations and I think I saw it on Dateline.
Have the date and time you were there when you complain. That should be on the receipt. They should be able to figure out who was working from that. Most corporate retail places I have worked the manager had to keep and/or submit copies of the schedule every week. Also you better bet payroll knows who was working when.
I remember from my days in retail, we always hated a complaint that went through corporate. And yes, believe me, just getting a mild 'don't let it happen again' is a big deal when it comes from above, especially for a manager.
I try to compliment by e-mail every time I see excellent customer service, because I don't think that gets recognized often enough, so I never feel bad about complaining when I have specific information.
Usually they will send you a form e-mail back so watch your junk mail. But I have received personal e-mails and phone calls from corporate heads.