Deposit not yet refunded

I hired some crockery for a small function on the 12th August 2017. I paid the amount for hiring and the deposit of R500 (which was more than the actual hiring amount). I returned all items intact on Monday the 14th and was told my deposit will be refunded to me within 5 to 7 days. It's now the 28th August and no deposit. My emails have been ignored now. Why would such a big company hang on to such a small amount for so long? This is not the first time this has happened with a deposit not being refunded.