Infinity flooring

We had a custom shower built several years ago. This person did the floor and the shower install. Used a grout that was defective and started crumbling a year after installation. He came back. And redid the grout with the same product. Same problem again after a year . When I called to have him look at it he said he was too busy to deal with it and it wasn't his problem. So fast-forward to today. We have crumbling grout. No one is particularly interested in fixing this . This was and is still a disaster.