Fissler Pressure Cooker Whistle Malfunction

I purchased a Fissler pressure cooker, and on the first use, the whistle didn’t work, and the cooker didn’t pressurize. It leaked air from multiple spots on the lid. When I requested a return, they refused, claiming it had been used. How else am I supposed to know if the product is defective without using it? This is frustrating. Products bought from N11 are becoming increasingly problematic, and N11 avoids taking responsibility for the issues. This experience has been disappointing, and I feel let down by both the product and the service. It’s unacceptable that a new pressure cooker fails to function correctly and that customer service offers no real solution.