Rotten mackarel from Checkers vergelegen Plein

I bought 2 mackerel fillets from the Checkers at Vergelegen Plein yesterday, the fish fillets were vacuum packed, and this afternoon when I cooked the fillets, I saw that the vacuum packaging was not as airtight as it had been yesterday. I cooked the fish, and took my first bite, which was horrible, the fish had been seasoned in store, supposedly a black pepper and salt seasoning.... So much black pepper powder, that the whole fillet tasted horrible, in fact I lost my appetite after a few bites, I still feel nauseated, which leads me to wondering if the people who prepare this had any training at all? I am still wondering if their stock is fresh, as I am now also worried about food poisoning...