Terrible Service

I have booked a flight from Cape town to Johannesburg for 17:30, (details below). I checked in online, I arrived at 17:00 to board. I was told it’s too late and never given options for another flight. They told me I forfeited my ticket and money! I was left stranded at the airpot. The customer care consultant was very rude to me and not sympathetic or offered options. Very very bad experience I had today. I would like to request to be reimbursed.