Change flight time without prior notice

I booked a flight from JHB to George on 06/042015 at 7h05 and upon arrival at the book in queue at about 6h45 a lady presumably working for Mango walked to me and asked which flight I'm booked on. I told her George. She rep**** that the George Flight were closed and I had to report to another service desk of Mango. The lady at that desk told me the flight was for 6h45 and not 7h05 as per my confirmation. Back at the booking desk a supervisor named Rejoice confirmed that the flight was 6h45 and not 07h05 and wanted to see the confirmation. I showed her the confirmation on my phone and she simply rep**** I was late for my flight. I told her I was in the queue at about 6h15 and she rep**** it could not be possible as she personally called before she closed the bookings for George. When I asked her at what time she made the call she rep**** at twenty to. When I asked her twenty to what she rep**** twenty to seven and after helped right by a co worker, changed her answer to twenty two pass six. She arrogantly told me I was late and had to book another time with Mango. When I asked to speak to a manager I was told no manager was on duty. She was very un-helpful and arrogant.