Chicken Burger instead of Vegetarian Burger!

Terrible service from McDonalds at Kyalami. I ordered 2 vegetarian burgers for strict vegetarians! My daughter was horrified to discover she had taken a bite out of a Chicken Burger! I’ve tried calling the outlet (twice) as per the contact number on the receipt to notify them of the error, and there is no answer. Terrible service and absolutely no regard for customers dietary preferences. McDonalds has lost this customer for good! Utterly disappointed!