Disgusting prawns

If I could give Seafood market Alpine road no star it would be great. I purchased 8kg prawns from seafood market Alpine road and when I made the prawns for guest it was off. I was in such a panic and had to order another 8kgs prawns from Checkers because my guest expected the prawns. I returned the prawns after keeping it in the freezer the next day and the owner refused to take liability for the prawns because he said his store policy is once you leave the store items cannot be returned. These were frozen so how would one know these prawns were off. My neighbour had the exact same situation a week later with the same outcome of 10kg prawns. These prawns cost were over R1500 so you can only imagine what my neighbour lost as well. It is unacceptable that the store would not even replace these items. I am a single mom of 4 and lost my husband. These prawns were for my daughter who graduated with her degree and all she wanted was a prawn meal for supper as we do not get to eat prawns often. I saved 4 months for this occasion only to be *****ed by seafood market Alpine road.