Refusal by Postnet to accept payment

I went to Postnet Glenwood Village, Durban to courier books to Pretoria from Durban. The attendant who assisted refused to accept the "old R100" notes as payment. I enquired as to the reason for this refusal and his response was that it was the "owners preference ". As far as I am aware, these notes have not been discontinued by the South African Reserve Bank and therefore is still legal tender in South Africa. It became inconvenient because these notes were issued to me by Standard Bank not even 10 minutes prior. Postnet Glenwood Village needs to be compliant with our current legislation.