False promotional label

This retailer advertised a special on Omo washing liquid - purchase any 2 1.5litre bottles for R79. I took two of the new 1.5l varieties to the cashier and was told that the new bottles were not part of the deal. This exclusion was not specified in the label. They would not sell me the products that I wanted, but rather offered me a rain-check on the 'valid' bottles, which were out of stock. If a product is validly part of a promotion according to the *label*, the customer has a right to purchase it as part of the deal.