Refusing to sell products as displayed in Window

Yesterday I went to STERNS N1 City to purchase a watch for my daughters as a Matric completion present. I saw a beautiful watch with bracelet set in the window and asked to view it, upon the store clerk removing the watch from the locked cabinet I was told sorry the bracelet is not included, even though it clearly set part of a set, I then said to her how is that possible as you have it in you locked window as a set, now that I want to buy it you say it is not. The manager was called, and her answer was the same, I phoned head office yesterday afternoon and had no feedback from them. I would understand if the watch was in an open space that a client could have placed this, however it was locked away no way that this was just a mistake. I had no choice but to purchase the watch as I still needed to get in engraved in time for her walk out day Friday, however I cannot see how they can clearly advertise it in the window as part of a set and then refuse to sell the set to me as advertised, they could not even show me the watch that was part of the set?