Costco please help!

I had the worst experience on Sunday. I was shopping at Costco with my mom. She and I were standing in line at the register. I saw the cashier go over to the next register and tickles the cashier. (First of all, she was very unprofessional. She was not supposed to be tickling other people while working. Secondly, to tickle at the workplace is sexual harassment? Am I right???) What bothers me is that she was not paying attention to her job when she placed items in the wrong cart. She rung up my cart with the other customer's cart. I said that she put the wrong items in the wrong cart. She said that I was yelling at her. Ha! It's the other way around! I had to apologize to her many times because she was raising her voice and causing a scene! SCANDALOSA! I felt I was verbally abused by her. Her name is Sonia M. Not to bore me or people who accidentally clicked on this website, but the whole argument escalated. She made many mistakes on the register. I logged onto Costco website and I could not find a drop roll for complaints and comments. However, I wrote a letter of complaint on Sonia M. who works at Costco, Tracy, Ca. I pay membership to shop at Costco, but I don't remember the membership comes with verbal abuse??? I want to appeal to Costco staff officers to intervene. I want Sonia to get customer service training. I want Sonia to seek anger management. More so, I want her FIRED!