What is the R25,85 fee that the South Africa Post Office charges on postal items?
The CN22 code R25,85 charge is a Post Office Assessment Fee and not a SARS Customs charge. As per the Post Office website on page 18:

Do I need to register as an importer if I buy personal goods from abroad e.g. from Amazon?
No, you don’t have to register as an importer if you meet certain conditions. Personal goods can be cleared with Customs under the generic code 70707070. However, you must meet the following conditions:

​My parcel has been stopped, what should I do?
In the event the goods or parcels have been stopped or detained, the SA Postal Office informs the sender or recipient of the outcome of inspection as well as the conditions or terms that must be met.