POSTNET GOVERNMENT ADDRESS SURCHARGE

I wanted to send an application for employment to Pretoria on an overnight courier and was told that the price was R185.00 from Durban to Pretoria, but since this was a government building I would have to pay a surcharge of R265.00. The lady explained that if the parcel was going to any other residence or company it would not attract a surcharge. Why would POSTNET charge R265.00 only because the address is a government address and yet it does not do so when I send the same parcel to a private company. This is clearly victimisation or opportunism against us seekers of government jobs if I can apply to Coca-Cola and not be charged a surplus and be charged a surplus even if I am sending a document to a municipality. Postnet is being discriminatory and unfair in its business practice, to the detriment of people who need government services. Why is there a surcharge and how is the figure of R265.00 reached and what is it meant to mitigate?