British Airways/Qatar airways/Comair

I had connecting flights from Budapest to Doha, Doha to OR Tambo and then to Port Elizabeth. My main airline was Qatar Airline, But my connecting flight from OR Tambo to Port Elizabeth was with British airways, opperated by Comair. My max luggage weight was 45Kg and 2 bags to check in. 4 weeks before my flight, I changed my flight from OR Tambo to Port Elizabeth from Saturday to Tuesday. On my arrival at OR Tambo I went to the check in counter and the guy attended to my check in says to me that I am only allowed 23kg and 1 suitcase. I told him my situation and he called his supervisor. She told me the same story and the harder I tried to explain to her that I already paid for the trip, 2 bags with the 45kg, the more she wanted me to pay in. I said to her, that when I changed the ticked, that I must have been informed of the price change. All she said was, sorry you should have read the conditions? I must say that in my opinion, this is not exceptable and very poor servive.