Internet usage seems...excessive?

I have a mild concern that our internet usage has goine through the roof lately - almost doubling in download over the last couple of months.

For clarity - I haven't checked this in some time, but when I did last check, we were on a copper 10mps connection and now we are on fibre 100/20

This month, we have the following useage stats:

Total usage to date: 390.32GB

Average daily usage: 24.39GB

Predicted monthly usage: 732GB

I have a pre-teen and a teen using a PC each and a mobile each, both play online games (mainly Fortnite)

Wife and I stream the odd bit of Netflix or iTunes (not a huge amount) and a bit of facebook etc.

Not a lot of IOT devices in the house - a smart telly, smart BD player (plus the usual 4 phones, 4 ipads, 4 computers etc) - no connected fridge, smart home devices or anything like that.

Whilst we are on an unlimited plan, I am concerned that the usage seems a little high and that possibly we are being tapped by a neighbour?