Trading in Bad Faith

I wanted to buy a cover for my Kindle from this company. They offered a R50.00 discount if you signed up. I did that, but didn't get my discount. I wrote to them and someone named Kim rep**** with a code. Well, the code seemed to be a link, when I clicked on it, but it died every time. It was also not accepted on the website when I went to buy the item and entered it. I wrote back about 3 times without getting a reply. Eventually I phoned and spoke to Nosipho. She assured me that I would get the R50.00 repaid to my credit card if I sent them a mail with my order number. At the same time I received a 5% discount voucher. I ordered the item, using the discount voucher. When I then wrote I was told the matter was resolved. I wrote again, explaining the sequence of events. I received a mail saying they did not voucher stack, so could not give me the R50.00 but giving me a voucher number to use on another purchase. Well, as you can imagine, there will be no other purchase from them. I would have preferred to use the R50.00 but was unable to do so. They are trading in bad faith.