Bad taste burger

Sunday 29th of October, we went to McDonald's in Krugersdorps, I bought meals for my family. One of my family members opened one of the big Mac meal I bought and at that moment, there was a smell but she thought it was just her nose, she took a bite but burger was off, she passed me the burger to taste, I also tasted it was off. I called the restaurant immediately but their number wasnt going through. I went to the McDonald's website to put a complaint and to date, there's no feedback, just emails with reference a d that they will get back me. I still have the burger for them to also taste the quality given to their customers and the receipt. I'm extremely not happy about the experience my family went through and the food quality given.