Misadverti*****t

On the 4th of december 2015,I made a booking and a SAA flight ticked was purchased at the cost of R1531,72 at shoprite store.the flight I booked was for the 5th/12/2015..on my ticket (flight no-SA2110Ref No-W15125NWROSW) it stated that SAA flight From cape town to durban,flight was scheduled to leave at 8pm but when I got there to check in an assistant working for SAA told me my flight never existed there is no flight going to durban @ 8pm so I'll have to add R1676,00(flight no-SA 1855 ***) more for the flight that's going to durban the next day 06/12/15 or else I'll loose my money because there will be no refund..I stood there not knowing what I should do because it was late and I couldn't understand why there's no flight to durban but I booked a ticket ,I tried to explain but the lady told me sorry sir we can't help you :( out of desperation I added more money so I endend up paying R3207,72..my main question is why did they advertise a flight that's not available what if I didn't have the extra cash was I going to loose out for booking an advertised ticked? I am very unhappy with the service I got from SAA as a customer!:(