Why does Discover Card lie about where the card is accepted?

My Discover card is my main credit card and it isn't accepted everywhere; however, if I got a card from them that a particular business took the card and it didn't, I'd call the number on the back of the card and complain. I'd email them or write a letter if I wasn't given a good explanation. It could have been an error, another branch of the business might have accepted the card, they might have canceled their contract. I don't think that pi***** you off is a good business tactic. Find out what's up.