Customer service sucks

I went into the store to refund something I bought at another Shoppers and was told that since they don't sell the product (cereal) that they can't take it back. I was overcharged for it at another store. The sales clerk was not helpful at all and just laughed at my disappointment and told me to read their refund exchange policy. He was mocking me and wasn't at all apologetic of the hassel. Never going to that Shoppers again!