Rude Manager

I bought a chicco bed rail from your store in durbanville 7 days ago. It was the last bed rail available in the store. I took the bed rail and put into my sons bedroom as I was waiting for his new bed to be delivered, never opened the bag or even touched it. Yesterday I took it back to the store were I purchased it and told them that I will exvhange it for something else then the store wont loose a sale. While busy in the store a lady came up to me and told me that her manager wants to see me now and that I should come with her.... Like a naughty child to the principals office. Got to the till and this old blond lady in a very rude manner told me that she cant take the bed rail back seeing that the packing is dirty, when I looked at the packaging on the buttom in one corner there was a little bit of dust that you can clean with a cloth. The bed rails are stored on their floor in a bin, the dust was only on the one side where the feet was standing on the floor. I told her and said that was the last one, i bought it and put it in my childs room. She rep**** sarcastically that there is no way that they would have sold it to me like that. My husband said to her, its a small piece of dust lets just wipe it, no she rep**** I cant clean everyone's return. The way she spoke to us infront of staff and other customers were really shocking. We also got upset with her, which we could have handled better but to talk to us like we are children is just not on.