Metro

Every time I go to metro they are problems. This time, I got reduction tickets, giving by metro before Chinese New Year. For each 388 rmb spent, get 50 rmb reduction. I give the tickets, the cassiers scans all my goods, then I remind her the tickets. She forgot about them.  My total is 1200 rmb. She can not give me 150 rmb reduction.  She needs to cancel everything, then scan until 400 rmb, give me the 50 rmb reduction. Make a second invoice for the next 388 rmb and a third invoice.  Then I'm wondering , what kind of idiot thought about this system?  It will take again some months before I go back to metro .