Bad service and failure to pay back change

I placed a Cake order two weeks ago, I have been calling the store to check if everything is ready for collection. They don't keep any record even when the customer has a Reference number I was asked a thousand questions every time I call even with a reference number that means it doesn't mean anything to them. I paid a deposit of R320 on Friday the 07/08/2015 for a R640 cake, On collection they advised my sister that the cake ordered was R280 and fully paid. they didn't bother to give her the difference of R40, when she went back after a minute to ask why a different order and why was not given the difference? the Lady gave her R20 and advised her to Leave as she was about to lock up. I cannot believe that anyone running a business can be so rude over the phone then don't deliver on a simple order not to forget the decency of paying pack what's owed back to a customer. I will never ever place any order with them again. I'm Hurt and disappointed of the worst service ever.