Mango appalling customer service made me lose my flight and my critical doctors appointments.

I'm an intern working in CT and I don't get to see my family in Jhb at all. This long weekend was my only time to see them and attend to all my critical issues. On the 20th September at 13:00 I was on my way to Joburg from Cape Town. I changed my flight time the day before telephonically to the earlier time with no problems as I paid for a flexi ticket when booking for my flight. I got to the airport at 12 and went straight to the counter to check in. They got my details and told me that I owed them an outstanding amount of R1800 because I had changed my flight. Because of this they refused to let me on the flight even though I kept telling them about the call I made to them the day before and how the lady who helped me over the phone insisted that I had no extra amount to pay. They refused to help me and sent me to guest services which then made me miss my flight completely. I explained my situation to the staff at guest services and asked them to put me on the next available flight. They refused to give me another ticket until I paid the extra R1800. I refused to pay as I knew that I had no outstanding amounts. They then called the call centre I had phoned the previous day to listen to the recorded call. After waiting for about 45 minutes they proceeded to tell me that the call I had made the previous day didn't state that I had no extra amount to pay which was wrong. Knowing no one was willing to help me I decided to call the call centre myself. I spoke to a friendly lady and explained the entire situation to her and I gave her my number as she was going to go listen to the call I had made the previous day and phone me back. She called back after 25 minutes and told me I was on their website the day before to change my ticket to which I explained that I tried doing it on the internet but it was not user friendly therefore I abandoned this idea and proceeded to phone the call centre. She then understood that a mistake had been made on Mango side and proceeded to arrange me to board the next flight at 16:05. She then phoned me back 15 minutes later and told me I was on standby for the flight as it had been overbooked. She then told me to find Lunga at counter 91 as he would explain the next steps. I proceeded to counter 91 and found Lunga, a very rude and non-helpful person, not just to me but other passengers as well, and asked him for my ticket. He told me to wait and I stood there for 45 minutes before being attended to. I eventually got my ticket and was almost late to my flight.