Very rude and unmannered

I went to Makro liquor and paid for the items at the till. The lady assisting asked if we needed a bag and I requested for one. She however forgot to ring up the bag. When we were leaving the store, the security at the door said that I was not charged for the bag. She asked do I really want the bag and I said of course. She then said I must go to the till again to get the bag charged to me. I was so upset as this is not my duty as I do not work in Makro and I am a customer. I went to the till and was told that I need to give the slip. Now at this point I am doing the employees job by walking up and down for a damn plastic bag. As I was waiting a guy, also a staff member, came past and made a comment \ek wil nou net gese het wat soek die laaities hier