Where are you getting that particular measurement from?
I’ve only seen the landing page, but that seems likely.
I know that Netlify err on the side of keeping your site up, and don’t yet have any kind of “billing limits” or “kill switch” - but that wouldn’t help you determine the root cause anyway.
They usually point people to this support guide:
Or suggest that they implement Edge Functions as per:
If you’re on a paid plan, (which I’d imagine you are with that level of bandwidth used), you could reach out to support directly via the support form:
https://www.netlify.com/support/
When this user reached out to support they found the site was being repeatedly crawled by Bytespider
https://answers.netlify.com/t/my-site-mostly-text-is-now-using-up-lots-of-bandwidth/113574