Cold and stale burger

Yesterday, the Coco Safar Restaurant served me the worst burger I have ever tasted. To start with, the dish was almost cold. Second, the bun was so stale, it could not be eaten. I confronted the manager with the dish, so he could see for himself. He confirmed the poor quality, apologized and promised to speak to everyone in the kitchen. At the end, neither a reduction of the bill nor a free coffee or drink was offered.