Bad burger at KFC

Had such a bad experience at KFC Jansen Park this week. I ordered a krunch burger. Barely left the store and opened the burger and it had such a foul smell. At first I thought that maybe it is my imagination so I took a bite and it had the worst taste ever. Went back to the store to complain. They asked for my slip and gave me a refund with no apologies or anything. I went that evening and complained on their web page. Received a call the next morning and was asked for the slip number. Told them that the store took my slip and never gave it back to me. They then told me that the matter is closed as there is no slip. How ridiculous is this. The staff keep the slips for a reason when you go and complain so that there is no consequences for them. What an amazing system. I told them that I had to complete a form in store with my complaint but they would have none of it and just said without a slip the case is closed.