Excessive baggage charges for children

I travelled from Durban to London on the 31st March. On checking in, we were told that we had to pay excess baggage charges to transport my daughter's car seat. I explained that my daughter is 2 years old and it is a requirement for her to travel in a car seat but the 'supervisor' at Durban airport was adamant and actually quite rude saying this is the requirement and we should have been charged previously. I explained to her that if I can't bring the car seat my daughter is not safe travelling in the car both travelling from Durban airport or from London to our home. She said these are the rules and this is their policy and we must pay if we want to take the car seat with us. Please bear in mind that I have travelled the same route previously with my daughter on SAA since her second birthday which is in January and was not charged any excess baggage fees for taking a car seat. I actually am disgusted with SAA that we would be charged to take a car seat. Does SAA realise that it is extremely dangerous to travel with a child in the car without a car seat! That we have to pay an excess baggage charge to keep our child safe is terrible. Something must be done about this.