BA’s money making **** baggage

I checked in online 24 hours before departure. At check in at the airport I was advised that I was only permitted to take hand luggage on the flight. In order to check my bag in I had to pay R1200 & go through extra security. On boarding it became apparent that other passengers with the same size bag as mine (the one that the checknin staff insisted was too big to go onboard), were permitted to take them on board, but I was not. I am sure that BA will reply that this was the because of the terms and conditions linked to my booking - if a ticket doesn’t not permit checked in baggage this needs to be made very clear to the passenger. For example, when I checked in online, I was asked how many pieces of luggage will you have and I selected “not sure”. Why would it ask me this if you’re not allowed luggage? What it should have said when I check in online is “no checked in luaggage permitted”. This is just a money making **** on the part of BA.