Worst customer service

I went to Shoprite to return a multiplug and cord 5 min after buying it as the cord was short and they refused to take it back as the plastic that was packaged with was slightly opened and was told the can't take it back was not used or damaged as they didn't even wana listen to what I was saying, didn't even look at the till slip to see the time frame and was rude as the food manager even walked away whilst I tried to explain. Shoprite must take their staff to customer care workshops or courses to learn how to give best customer service. For some one who is working with people you can't be that rude. If this can't be solved Shoprite will loose customers.