plastic found in cake

We went to the McDonalds Amanzimtoti and the cake looked delicious, we ordered a slice of carrot and cheese cake. If was horrifc to find a peace of plastic string in the cake, when we took it to the lady at the counter all she said was they don't make the cake she will tell the supplier. I was piqued and horrifed about the way it was handled much to my disappointment, and never again.