Hey, you make a mistake

I had lunch at home this noon. And then I went to the China Mobile Business Hall to paid the fees for my cell-phone. One of my friends works there. Well, I went straight to her. Heh, she is a beautiful girl and she loves beauty very much. So at that moment she was still looking herself in the mirror and patting her face. Then I gave her 20 yuan for the fees, and I didn't ask for the invoice because the printer was broken. We just talked for a little while and then I left for work. When I came to the office, and turned on my cell-phone(It shut off because of lower power so I didn't took it to home), I received the message from the China Mobile. I was surprised because it said that I paid 50 yuan. Oh, my God, she must made a mistake. So I gave her a call to confirmed the information. It was really her carelessness. I said that I will give her the remaining 30 yuan after work. Heh, you girl, please pay more attention to your work. Otherwise, you may not only make mistake but also lose money.