Plastic in the Burger Patty

On the 2nd January at +-19h50 we went to SPUR (Gordons Bay) for dinner. I ordered a burger, think it was with guacamole and feta. Halfway through the burger, I bite into something hard, which was a thick piece of plastic that was embedded into the patty (20h23). The management proposed to make me a new burger and or not to pay for the burger, but I insisted that I would like to pay, as the comment from the manager was that "he has NEVER seen plastic in their food since he started there 2 years ago....". I did not eat the rest of the burger, no new burger and I did pay for the burger. I can share the photo of the invoice and plastic in the food.