I recently received a scam/spam email from email@example.com with the subject set to "Important: you're reaching your line's capacity" and claims in the body of it that I'm "connecting quite a few devices, and downloading a lot" etc.
This is extremely unlikely to be true in my situation (one person, one computer, no gadgets, no wireless, no gaming, no significant streaming) and the email contained no evidence to back up its assertions. It's very clearly a spam email sent out to everyone, regardless of their individual circumstances, and is just a scare-tactics marketing scam - despite it also claiming not to be that!
However, I did go onto my account page online to see if there *was* any evidence of broadband etc usage monitoring (in the same way as one might see itemised phone calls) and couldn't find any page presenting any stats which TalkTalk might plausibly have been collecting for my individual account and broadband connection.
So, if TalkTalk *does* do any sort of monitoring of people's individual line usage, it would be a nice feature to have it visible to the user themselves on their personal account page. It could possibly occasionally be helpful in tracking down whether anyone else is hacking into an account, eg for those people who have insecure wireless router connections or are infected by bitcoin miners using their computer systems while they know they themselves were not active online in any form.