Laptop out of stock twice

I visited Vodacom branch in Midlands mall in Pietermaritzburg to apply for a laptop contract that I saw advertised in January this year. The brand was Acer and it was going for R299 per month.We did some paperwork and I was told to come after 3 working days to collect my laptop. A week later I was given a call and was told that they don't have stock anymore but they can give me another brand for R350 per month and I said let's cancel the deal cos I felt this was very bad service to their loyal customer who had spent about an hour in the quee to make that application. And then again on the 21st of March 2016, I decided to go to Vodacom Westwood mall in durban to make another application. They again have advertised an Acer. I made an application and was told to come back after 2-3 days. I went there yesterday (all the way from Pietermaritzburg) only to be told that it is out of stock. From there I concluded that Vodacom advertises products that they don't have! Can somebody explain this! !!