Could have done better

Went to the restaurant Saturday evening with 3 of my friends for my birthday lunch, the starter was great and the services by the waitress was good. We all ordered the same main course meal which was a lamb shank, the meat was off and we brought this our waitress attention. She then called the manager who was exceptionally rude, who treated us like we where not paying guests. He offered offered no resolution and only promised to call me on Monday once the head of had tasted the meat its Tuesday night today but im still yet to hear from the restaurant