Hartz flea spray

We lost one of our cats dusty due to the flea spray, he convulsed and fell over and died infront of his owner, dusty was a wonderful yellow tabby cat and was fine til he was sprayed with the product, Jr our other cat, was also sick too from the spray, he had to get IV fluids cause he was sick from the flea spray, thevet bill alone cost 183$ but losing dusty has been a major loss to us,