You did nothing wrong. Perhaps it was an innocent misunderstanding that they interpreted as deliberate. I would have gone back to the store and asked to speak to the manager. While it wasn't their fault, I would have asked to be escorted to my car because I felt unsafe. The store won't like having that kind of problem and should begin to monitor things more closely and intercede on good customer's behalf.

What they did to you (if it was deliberate) was racist. It's there problem, not yours. You did nothing wrong.