Burger King Gave Me an Incomplete Chocolate Milkshake in a Soda Cup

I went to Burger King to get a chocolate milkshake. Since they didn’t have a large cup, the employee poured the milkshake into a soda cup but didn’t fill it completely. When I realized the cup was only partially filled, I immediately pointed it out. I explained the situation, but they refused to acknowledge it. On top of that, although I had specifically requested chocolate sauce, they didn’t add it. It was clear that the service quality did not meet even basic expectations. I ended up being disappointed despite paying for it. This incident happened in Silifke, Mersin. Even though I threw away the receipt, two of my friends witnessed the situation. Unfortunately, I no longer consider choosing this brand again.