Discovery Travel / BA are absolute *******

Unbelievable! I booked a flight through Discovery Travel; BA, from CT to Durban, and another flight back. I had to do the first flight earlier than expected as my mom is in hospital for an op. I phoned to try and change the flight, but it was cheaper to just book a new one; which was also with BA ironically.

I am meant to be flying back to CT tomorrow; when I called BA to add another bag to the flight, they said that my flight (just for me) had been cancelled, as I didn't take the "first leg of the flight"??? ***; since when are flights more than individual flights within South Africa? This is complete *******. I paid for a flight from DBN to CT, and I expect to be given the flight THAT I PAID FOR!!!