At the two-yuan store downstairs, I was self-checking out and accidentally scanned a pack of trash bags twice.

I went to the cashier and said I was overcharged and wanted a refund, but the clerk took a look and said to keep that pack for now, then refused to give it to me.
I said I lost five yuan, and he said that’s not right, I must have made a mistake.
Later, I explained several times in front of the counter, and he finally called over a colleague who could understand, and they refunded me the five yuan along with the trash bags.