Selling item out of stock!

On 31 March 2016, I app**** for a Zte MF65 Mi-Fi Router on a SMARTDATA 5GB (GIGA20).Being an existing client, my contract was approved within minutes - thank you cell c call centre. I was told it will be delivered within 3-5 working days. After a number of calls and 15days later...i keep getting the feedback that the item is out of stock. Why sell an item out of stock?? I could have taken another deal with the another network an be satisfied. Cell C - please resolve this issue asap or cancel my contract. I really expect much more more from Cell C!<br>