Breach of contract

Supplier quoted for skylight DIY kit at R2650 with discounted rate at R2500. I agreed to purchase and asked for pro-forma invoice to make payment. Supplier sent quotation for R2600 and when I queried he told me that he changed his mind and was not willing to sell the skylight at the rate quoted. When I complained I was told that the topic was not negotiable. This is breach of contract and an indication of the ethics of the business.