Disgruntled customer

I purchased what was supposed to be 1st grade polished porcelain tiles from Malls tiles in Durban. They were not what I paid for which cost me R15000. The tiles are developing stains on them from beneath the tile which cannot be removed. Malls tiles manager came out to inspect and tried to remove the stains but failed. They since offered to give me more tiles to the said value. Why would I want tiles from the same place that sold me defective tiles to begin with. My labour cost is not even included. To remove and replace the tiles they say is at my expense . Unacceptable.