British Airways charging exstra on Buggage.

On Monday morning we flew back from Port Elizabeth to Johannesburg. BA 6248 When we booked in for our flight we were informed that our Suitcase is to heavy. 28kg. Our Suitcase was for me and my wife. With Mango that we flew to George it was not a problem. With British Airways we now had to pay an additional amount of R340. We did not receive any transformation limiting us to the minimum weight. Is this how they make money or how does it work. To me it is very unprofessional, and it feels like they joined the rest of ******* South Africa to make money from the paying customers.