complaint

I am a cashier at shoprite glen, on the 3 September 2015 I was working on till no: 9 a customer came to pay a few items while she had other groceries and I asked her what about the other groceries she said she had already paid for them by another till so I let her pass after ringing uo the items she gave me, she was stopped by securities at the door after they checked the slip they saw she paid by me they asked her and I told them what she said, then the regional manager Mr. Pillay instructed my manager to get me arrested i slept in a prison cell i went to court the next day and the court said i didn't have a case and u was released, i went back to work on the 5th and my Admin Manager Zandile Dlamini said i was suspended pending an investigation. i want to know as is it fair that I got arrested for doing my job, if I had argued with the customer I would've been in trouble again.