No customer service. Don't care attitude

I went to Pick n Pay Hyper in Greenstone where they were having a 20% off if you bought two of particular product before 11. I arrived at the till before this time and informed the cashier that I would like to qualify for the % off. She said they were busy with a shift change and I would be assisted as soon as possible. As soon as she put it through which was 11:02 she said I didnt qualify because it was 2 minutes after time. She called a manager over who told me there was nothing they could do and the whole attitude was that it was my fault. I explained to her what had happened and she didnt care and that I should have requested it. No apology. No care. Will never shop at Pick n Pay Hyper again