How do I deal with bad customer service?

Today I went to Zellers to shop for deals and found that they had items that ranged between $1 to $3 for 50 cents (they were mostly school supplies and locker accessories) so I choose a couple of items and purchased them. On my way out I noticed that I was charged 75 cents for each item instead of 50 cents. So I went back to the same cashier to get the amount adjusted with the sign showing the sale. When she saw the sign she stuck her tongue out at me and refused to adjust the price saying that these items were not the ones on sale, and a guy behind me swore at me and said he'd me more than willing to throw the difference in cash at me, so that I don't delay the line up (the customer service section was closed) and she sided with him. I didn't say anything. Another cashier came and said that these items were in fact part of this sale and she did the adjustment, but no one apologized. Its not about the money (the difference was a dollar), its about honoring the sale. If I had bought 10 items, that would've been a difference of $2.50. A dollar to someone who's on low income is a lot of money. So what should I do? Thank you.