Not honoring promotion. Robotic sales manager.

Went to buy some lighting products. There was a promotion which stated "Buy any 3 lighting product and get the cheapest one free!". The store refused to give me the promotion as they stated it was only from a certain selection. The promo banner did not mention this in any way, the text "ANY" should apply to any products. Further the sales manager Nicholus from the Rosebank branch in Johannesburg was not client friendly in the slightest. He simple and bluntly told me to take it up with head office.