I don't know if I agree. The problem is trying to use the analogy that the etoll bill is like a fine, which is not correct. A fine is imposed by enforcing body, which if paid, would result in that body not pursuing criminal charges. You are not obliged to pay the fine, and you can't be convicted for failing to pay the fine. You can have your day in court arguing the underlying speeding offence, at the risk of a criminal record and the imposition of a fine (that is, issued by court) (including jail time, if warranted). [Note I am not dealing with admission of guilt fines.]
SANRAL have done the opposite: At all stages you owe SANRAL the etoll fees. But if you fail to pay your etoll fees, you commit a criminal offence. So you can be guilty of failing to pay the etoll fees, and SANRAL can issue civil summons against you ensuring that you pay your etoll fees. Essentially a double punishment.
This is, at least, how I see it.