Family Dollar complaint: Return complaint

I went to the store and purchased a manavox car cassette adapter.. Went to my car to plug it in.. It did not worknfor my car.. I went back inside with my receipt maybe 2 minutes after purchasing.. The women said asked whats wrong i said it didnt work for my car she said sorry all we can do is exchange it.. They have a sign on the inside that says only merchandise with a receipt can be returened or exchanged.. (Open or unopened) it was opened. She would not give me her name which it should be displayed on her shirt or on the receipt.. She was extremely rude and I will not be coming back to that location.. She does not know how to speak to people or wouldnt do anything about my purchase.. Honestly she should be fired for the way she handled the situation. She wouldnt even allow me to exchange it for another item in the store for the same value