Edgars Canal walk shocking

Yesterday evening I walked out the door of Edgars and the machine beeped. I had unknowingly walked in with a t shirt that I bought a few days ago which still had the barcode sticker on. Had the machines beeped when I walked in the store I would of known that the irritating thing annoying me was not the tag but the barcode of the shirt I bought days ago at another store. It was so funny that the machines could beep when I was leaving the store but not when I was entering. Because of this I was stopped by the security as they were alleging I stole the item .I explained to the security guard how could I have ****** the item if I have nothing else on me did they think I walked into the store topless and stole a sweater and walked out. My character was defammated I was publicly humiliated as the people in the store and walking past thought I had stole the item.I video recorded the whole event and when I was taken to the room to look at the footage I was told I cant video record I can only voice record from there onwards. The footage was only found after nearly and hour and the manager confirmed that they did not have stock of the t shirt I was wearing. I am now considering civil action.