Unfairly treated

I have never been so embarrassed in my life. It was on Sunday morning I went go buy groceries,it just so happens that when I got to the till,I received a call and got distracted a little bit. I mistakenly put a chocolate in my purse while looking for my card to pay,I paid R1200 for all my items not being aware that the chocolate was in my bag. When I got to the door, the alert sound came on. I started searching myself and the plastics that maybe something might have gone through by mistake. I realized it was the chocolate in my bag which I was not aware I put it there. I asked the securities to quickly go and pay for it as it was an honest mistake. They let me pay but when I came back to my trolley they took me to the storeroom saying they were charging me. I pleaded with them saying it was a mistake and I have paid for it. I asked them that can I really spend R1200 at a shop then risk going to jail by *****ing a chocolate of R15. They showed me the CCTV camera which showed me putting the chocolate, I admitted to it but still told them it was an honest mistake. The supervisor told me they do not have cameras which can detect a customers mind therefore I knew what I was doing. He told me they will give me grace and let me go but I had to pay a fine of R200 which I didn't have but because I know how false accusations can ruin someone's life especially when it comes to the law,I had to call people to bring that R200 after being kept at a cold storeroom like a ********. I understand they had to do their job but I still feel I was unfairly treated and they were trying to prove some sick point. I buy my groceries at the store every month and have never had such an encounter. I felt humiliated and violated as customer.