Maize meal with worms

I bought Iwisa maize meal at spar 2 weeks ago. Last week I found worms in it. I went back to the shop and told them about that. I was told that because I don't have the slip or package they cannot assist me. As a big shop as they are the least the could do was find a solution they just told me they cannot do anything. I told them that they have cameras in the shop can they not review and see that I was there and I did but that product.