Bad customer service!!!

I went to buy my groceries at this shoprite store, when I got home I discovered that I was billed twice for a particular item. I immediately called the store to inform them, they told me they are about to close so I can come the next day to query this. Well I live just over 21 Kilometres from the store and driving there and back (42km) for one item would be pointless and waste of petrol. I suggested to popby when I'm in the area as its another expense to drive there for their mistake. I went to the store about a week later for my refund, when I got there I was told I must go home and bring the product because their slip doesn't specify the product so they wouldn't know which one is it and its impossible that something will be on my slip if I didn't buy it. Well I don't know if this is the kind of service shoprite offer to their customers. I am totally unhappy with the way this was handled. When I asked if they'd compensate me for my petrol seeing that they want me to run up and down I was told its not part of their policy, this was a mistake that I could have done it myself so I must just be understanding. Well I didn't do the mistake, they did and they must take responsibility.