Huge financial loss

On the 3rd of March I went to builders warehouse Gezina to buy paint. Their procedure is: A customer gives them the specifics or requirements of the paint needed, then they mix it accordingly after they mix the paint they hand it over to the customer for payments. I gave them specifics or requirements of the paint I needed, they are Exterior Dulux lilac paint. The person who was helping me collected the paint from the place we're they stored paint went inside to mix paint, he then went with me to the counter to pay for the paint after that accompanied me to my car and loaded the paint for me. On the 10th of March I went back to buy another paint, Dulux Golden Bark Exterior paint, only to find out that on the 3rd of March they gave me a wrong paint they gave me interior paint luxurious silk instead of exterior paint, I laid a complain with Bra Phill he said he will call me on the 14th of March but he never called, on the 15th of March I went to back builders warehouse Gezina and spoke to the sales Manager William Makua. He told me to bring the paint containers with me, so that he could speak about something that they see. On 17th of March I went to builders warehouse Gezina to drop off the containers, William Mokua told me that he will call me on Monday the 19th of March but he never called. On the 24th of March I went back to builders warehouse Gezina to enquire about my complain the RPL Manager Rozita Koekemoer told me that " they won't do my thing about my complain" with unprofessional attitude I have also called builders warehouse Head office no one is willing to assist me with my complain.I must suffer financial loss because of their staff member and they don't even care or even sympathise with me for the financial loss that I have suffered because of their staff member. that means the errors of their staff member it's my responsibility not their