Change of gates without informing passengers!

On Friday 28th September my husband and I had a company flight booking from Lanseria airport to Capetown. Upon arriving we went to the bag drop were we where told the flight is closed for checking in any luggage but our bags are small and can be used as hand luggage. We then proceeded through the luggage checking gate. Straight to gate 4, stated on our ticket. We stood in line. Go to the front whereby the lady informs us we are at the wrong gate and need to be at gate 5 but they have just closed the gate. I asked her how can it be gate 5 as the ticket states gate 4. She then asked another guy to assist and he told us its our fault missed the flight as they dont walk around and calling people. After his rude comment we were instructed to go to ticket sales. We had to get new ticket that totalled to R4700 for two people,one way!!! We then discovered there are 10 other people in the same boat!!! Now i ask you if my ticket days gate 4 and i am standing at gate 4 how should i know i am at the wrong gate!!! Kulula if you change your gate numbers how can you not have staff members checking at the original?! I will never use them or suggest kulula again. Money does not grow on my back kulula!!!