How to handle a business that overcharges?

I bought an item that was marked as $25. I ended up being over charged for the item. They charged me $32. When I returned they said the item wasn't marked correctly and really did cost $32. However, the business agreed to return the money on my card because it was their mistake. I went home, waited three days. (thank god I held on to the receipt and the tag off the item!) I looked online at my account today. They did not return the $5 they overcharged. Instead, they charged me an extra five dollars! This business owes me $10. What should I do when I go back to the store? Normally, I'm a nice person and I don't want to be rude. But $10 is a lot to overcharge someone. I don't want to let it go either. Do I print out a copy of the bank statement?Or just have it on my phone to show them?