Not official eight, but eight has pretty good deals, can say i am a big fan
I was talking about the need to Pre-Pay but they are still actually postpaid plans in the system, not pro-rating which depends on telco. As far as i am aware the only MVNOs that let you pay-later are Vivifi and Circles.
A lot of these Pre-Pay postpaid plans also just terminate your line (within a grace period) if you don't pay up, unlike a traditional postpaid/phone contract line where you can actually own them money.
It is mentioned in the CIS which you agreed to when you sign up. You can actually let these plans just "expire" if you really want to.
it is impossible to convert back from Postpaid to Prepaid. People here like to speculate for their porting mistakes, like ID mismatch, Wrong number, or didn't know that they violated some agreement with their existing telco (e.g. minimum 2 month stay)