defamation of charecter

I went to Spar on a Sunday morning around 5am on my way to work,bought vicks and when I got to the door the security searched my handbag and found my opened Orbit Chewing and she accused me of *****ing them. I told her that I came with them but I was told to pay for them...I refused to do that and the asked them to checked their cctv footage. That is when they told me to come later after they have checked it. I went back after work and was told to come in the morning. When I went back in the morning there were more stories. Why was I asked to pay foe something that they had no proof that it belonged to them? And if they were so sure that I had ****** from them then why wasnt I arrested? Whats going to happen to my Orbit chewing? Obviously they cant sell an opened pack. I had to ask lady to write a report on her OB book which she was suppozed to do if she was following procedure