Rude Cashier

I went to Brooklyn mall checkers and the cashier offended me. There was a note written "CARD ONLY". I joined the que because I was using card. She told the first person that she's only accepting cards, then when I approached her she said "Card only" then i said ok. After she said "This is what I have to do the hole day especially to BLACK PEOPLE they give me problems because they come with cash or ask for cash even when the note is there but WHITE PEOPLE they dont give me problems. This did not sit well in me I felt like we black people we are stupid, we can't read or understands English. I moved from her till and went to the other till. I was so emotional when i left the store.