Vodacom
When purchasing internet data bundles

Purchased 250g for R50 of internet time (on special) via prepaid cellphone. Put the cellphone simcard in the modem and connected to internet via pc. Browsed happily until internet connection stopped.
Assumed that the 250g had been used up. Put the simcard back in my cellphone and found out that there was nothing left. The pc did not disconnect when the purchased R50 worth was used up, but continued without warning until all the prepaid left on the simcard was used up. In other words spend R50 on special and they take up whatever is left on your prepaid simcard (at the regular price), without asking, seems like sophisticated.