Top T Lenasia sold me B grade tiles instead of A grade

Last month I purchased 72 square meters of porcelain tiles for 4 rooms. The tiles were one batch but different shades. We tried to match as best as possible but a few days after the tiles were laid, there were stains and water marks that absorbed into the tiles. Hence the 'porcelain' tiles which were supposed to be durable and non porous were exactly the opposite. I brought the manager from the store to have a look and he was also shocked to see the stains. He advised that it was a B grade commercial tile and we were supposed to seal it but they also didn't know. He contacted the supplier but according to his feedback to me the supplier says that once the tiles are installed they cannot do anything. I told him that the problem started only once they were installed but he says his senior offered to go 50/50 only. The problem is that this resolution is not feasible as I have already spent close to R20 000 on the tiling which includes material like cement and grout etc as well as labour and delivery. I spent my entire bonus on all 4 rooms already and it's not fair that I must take such a big knock for their negligence yet they tell me that they cannot take such a big knock. I also initially asked if these were A grade tiles when I bought them and they said that it was now they say it's B grade. Even the boxes show AAA grade, when I pointed it out to the manager of the store he said the original boxes got wet in the rain so they were using boxes for another tile. Their resolution is putting me out of pocket for reject tiles that was sold to an unsuspecting customer like me. This is very poor customer service for a mistake on their part.