I had the worst experience ever

I had the worst experience ever. Thabang, the manager, gave me a short change of 20cent. When I asked about it, I was told they don't have it in the till. I'll get it with my order. I've ordered a chicken salad with extra feta that had rotten feta. My whole idea was just to ask them to remove the feta n refund me for the feta. Thabang came with feedback to tell me it's not rotten, and that's how their feta tastes. I was trying to tell him with my management experience in a restaurant of 23 years. I smell and taste it's rotten. A young man of his mid 20's still **** to me, insisting it is not rotten, and he got 13 years of experience in a restaurant. As he knows, it's not rotten saying it with a bad attitude. I've instructed him to refund all my money and eat that salad he says is not having rotten feta. Clearly, he doesn't care about the customer or the reputation of the company. Bad customer service and rotten feta in product.