British Airways didn't provide a meal as it was finished

My parents travelled to India last week on British Airways flight. Both of them are pure vegetarian and were desperately waiting for a veg meal. But to utter surprise British Airways staff said that vegetarian meals are over and they can only offer non veg meals.

Parents had to travel without a meal and this has brought lot of embarrassment to me as I've sponsored their trip and planned everything.

Is there any way I can ask for compensation and what are the chances of that being honoured?