The cause of your problem is probabily that when the tile was installed they did not use tile backing board. Tile backing board is hard and does not yeild. Tile that is installed directly on to the existing wood floor will crack due to the give of a wooden floor. I just finished pricing flooring. It is actually cheaper for me to use tile. First the because the custom order flooring comes in twelve foot lengths, I would need to order a 8 x 12 piece. With tile I only need to order enough to cover the floor 70sq ft. The floor is not square there for the difference. I didn't want seams.