Postnet Summerfield ********* Business Practice

I was **********ly overcharged for courier costs by Postnet Summerfield in Boskruin, Johannesburg. I checked the waybill details with 2 other branches and one came in at a third of the price and the other, half. I understand that there are fluctuations due to different couriers being used. They don't input the details into the Postnet system (as, I understand, they should) and they 'work it out manually' using a calculator. I went to the store again to query this and the owner has not bothered to contact me. This is not only bad service, but ********* business practice.