Invalid Charges on Cargo Transport

4 months ago I obtained a quote from South African Relocations for my belongings to be moved from Cape town to Sydney. I received a quotation of R75000 for 26 boxes.

After the Invoice was paid on 19th of June my goods were picked up from an storage in Cape Town so it can be shipped. on 12th of July my Goods were sent by Singapore Air Cargo and while my goods were in transit in Singapore I received a call from South African Relocations that Singapore Airlines is asking for additional R58000 and it is because the airline can charge either by weight or by container which ever is more exe[pensive and in my case they decided to charge by container. To make the matter worse the containers arrived in Sydney in 2 separate flights and now the transport agent in Sydney is asking for additional $450 because they have to go to Sydney Airport twice to collect the goods. Now none of these two companies are taking responsibility for all these additional charges that I have to pay and I am a 65 years old retired single person.