Accused of *****ing

Bought some items from Pep home after paying my child wanted a sweetie took it then paid for separately as I was already paid for other items. Few minutes later realized I took a wrong size went back to exchange and my child still had that sweetie with her. Did the exchange and went. Received a call from the store to say I didn't pay and I better come back to pay tried to explain what happened to the cashier but she was not even willing to listen instead her colleagues were screaming and shouting \hey come back to pay\" went back to show the slip the lady just grabbed it and went inside their offices no apology or acknowledging their mistake and that was just it. "