Pathetic service from British Airways in East London Airport

I booked a flight from East London to Johannesburg and it was scheduled to leave at 12h00. I got there at 11j10 and I was told that I could not be checked in at the desk and will have to book another flight for tomorrow. I am not satisfied with the service I got from this airline and I believe I should have been served. This needs to be looked into as I have now lost money due to this pathetic service.