Mango cancellation

I had a flight for 9.40 to George from or thambo, I got to the check-in at 9:15 stood in the que for check ins and when I get to the checkin counter I was told that the flight is closed and I cannot get in. I wen to the counter where the lady informed me that I can reschedule this flight or change it for a later date, upon checking the website I was informed and the flight I want to change to is actually cheaper than the flight I had I still have to pay in +_R500, that's ridiculous, I then wanted to cancel my flight that was returning the next day and now they don't do cancelations, i am so disappointed as I have been a customer of mango for years and this upsets me also I am traveling from Mpumalanga and I don't dot have a car it was a complete hassle to get here.