Wow what a mess!!
How did you end up paying 10k for that disaster?!
I paid then up then went down the route of trying to recover, lesson learnt. I’ve since acquired some tiling tools of my own as I can’t afford to hire another pro. I’ve skimmed the walls, concrete filled and levelled the floor, I chucked a cheapo tile floor down to practice, the floor was done without proper tilers tools and a stone and masonry disc on my angle grinder only. I’ve now acquired suitable tiling tools and am getting ready for the bathroom refit. Pictures below, I’ve also added a picture of what was under his tiles, great big voids.