Free with purchase for some, but not for others - Mindstorms Mini Robots 40413

I recently bought Lego Mindstorms 51515, from Toy Kingdom. My son was very excited. We went online to see all the things that he could do with the new set. To our surprise we found that the 51515 set comes with a free with purchase Mini Robot set 40413, which we did not receive. I contacted the store and they responded that they have different working agreements with LEGO South Africa, and don't have the free with purchase set. I contacted the LEGO store in Sandton and they confirmed that they do provide they 40413 set as a free with purchase set for the 51515 set. I have looked online, and I cannot purchase the 40413 set as it is a free with purchase set. What perplexes me, is that both stores sell the 51515 set for the same price, but the LEGO store in Sandton has the free set and Toy Kingdom does not. I cant help but feel a bit cheated by LEGO SA, since they are the ones that set out the agreements with retailers. Especially since this particular Mindstorms 51515 set is at a premium price point. I did receive feedback from the LEGO support desk in the UK, who were unable to assist, not for lack of eagerness to resolve my issue though. I have yet to hear form LEGO South Africa directly though. So far just crickets....