British Airways is a ****hole!!!

I booked a return flight with British Airways from Port Elizabeth to Cape, last year already. Everything was confirmed. Now on my way back from Cape Town to Port Elizabeth, I get to the airport they say my flight is fully booked. What do you call that?! The service I received was so poor even the front desk people are cheeky and when I called customer care services they hung the phone on me. I want my full refund. This is very unprofessional and disrespectful. Will never forget you.