Oh gosh that sounds awful. I really sympathise. This is difficult! He does sound like a bodger - that comment about you not noticing is both cavalier and treating you like a fool. I would stop the work as Revolted said. If he is making a cockup of this then there are likely to be other problems coming up.
The best way to deal with him is to use the 'Sandwich" approach when you say that item X is good, and you like that result, but there is a real problem with the tiling and THIS is the result you expect (be specific) and ask how he is going to rectify it? Let the silence lengthen and get HIM to come up with a solution. If the solution is not satisfactory, bring the subject back to the exact result you want. Keep the conversation impersonal and about "the result" and "the work" rather than "you have gotten this wrong".
If he blusters, keep highlighting all the lovely work he has done, saying "items B and C were just fantastic, I really would like this tiling to be done to the same great standard you did on B and C, how can that be achieved?"
If you steer him a bit then eventually he will be stuck and have to admit that the tiles will have to be pulled off and redone. At his cost.
That would be the best possible outcome. However ... Unfortunately if he does not have the tiling skills (which I fear is the case) then you're not going to get it fixed properly by him anyway. In that instance, you may have to accept that you will need to live with the crappy tiling, and get it redone properly at a later date, and limit the areas where he works on your property. You will need to manage the quality of his work very actively from now on. Very difficult! I wish you luck!