False Advertising

On the 16th June 2015, I went to the Cell C branch in Kenilworth Centre to upgrade my cellphone contract. I chose the Samsung S6 with comes with a wireless charger. I was told that they didn't have any phones in stock and that they would call me when the phone arrives. On the 4th July I got a call to say that the phone had arrived and I could come and collect it, however I could no longer get the wireless charger because that promotion was over. I informed the sales person that I did my upgrade within the period of promotion therefore I should receive the wireless charger. She then said there was nothing she could do. My problem is this, why have a promotion on a phone that was not in stock (across the country, according to the sales person) and then when there is eventually stock Cell C can't uphold their end of the deal. Whether there was stock of the phone at the time is not the customers problem, I upgraded my phone in the promotion time period therefore I should receive all items promised by Cell C