I've never been charged for traffic I didn't use but their usage meter isn't real time and isn't on many ISP's due to the complexities of doing this. There have been numerous people on here post over the years, with many people complaining they go over their cap.
I've yet to read about anybody complain about traffic they haven't used, but the normal complaint is that they exceeded their cap because they thought they had traffic left when they didn't.
Looks like they've screwed up this month's billing or the meter is way out, or both. I usually don't look at my bill too carefully but fortunately I did.
They've charged me for 3GB additional usage ($8.84) this month when I only used 19.75GB of my 20Gb plan.
Looks like I'll be on hold forever on Monday morning. Will be interesting to see if they have improved their customer service as promised by the CEO on Fairgo the other week. Maybe they've had to overcharge everyone to make up for the extra staff to answer the phones.
I'll make another post warning everyone to check their bill closly this month.