Poor quality stone

I bought a quart stone from this people, Royal Granite tops in Germiston. I bought it in October 2020, on 28 June 2021 as I was dishing up the stone made funny sounds, when I looked I found that the stone has cracked. I informed Charles Matondora who is my contact there. He promised to replace it. Since June I have been following up with him. Every time he would make a promise that he never kept. I don’t know any stone that just break out of the blue. They must either replace my stone or give me a portion of my money back so that I can buy another stone. Hardly one year the stone is already breaking. This is not the way to do business.