A bad service at a furniture shop.

I'm a customer who bought a bed from this store called sleepmaster shop at Pretoria kwagga center on a blackfriday sale,the bad thing it was advertised on that friday with a cash of R3500 but the normal price it was R6000 so I pay them that R3500,00 cash , they promise me to deliver the bed on Saturday, they suprise me on Saturday when they told me that the bed is out of stock.When I went there,they told me that they can give me a cheaper one and there is nothing I can do.

On my opinion,I wanted the one that was advertised on the BLACKFRIDAY sale that is worth R3500.00.It would be a great honour if you help me with this issue. my contacts number ********** 933.