Hair in food

so Monday i took my son a nephew to spur for lunch. Waiter was very friendly. At first then my son ate some of his food but did't want food as he wanted to play.i asked the waiter to bring me a take way wag to put it in. To my surprise when i dished the food over i found fried hair in my sons chips. The waiter then went to show the the manager where one of the manager came and said sorry then said that they will cleaning the griller and the hair of the brush went onto the food..i then asked him what was the food doing by the griller if u where cleaning it.don't u sanitise the place first he then didn't respond i then told him that i will not pay for my sons food he then told me that its not a problem he will replace it for my son as well can put it in a take way box the waiter then came back and i explained this to him he then brought a different manager who was very rude showed no empathy. And told me they will not replace iy and give the meal for free. They will take it back and then take it off my bill i had to take the food from my son who later asked for it barring in mind his only 4 to take it from my bill waiter then doesnt come back. I had to ask someone else for my bill.