When fibre was first launch there wasn't a billing component of it so anyone who chose to be on the 100/50 plan was actually getting unlimited interwebs and getting a credit to take them to the 30/10 plan price ($95 from memory but I could be wrong).

The full billing stack is now in place (I should know as I built the subscriber management and throttling stack, so blame me for why the good times ended).

So if you are on an overage plan rather than capped, you may have been charged for overage on the month.