Actually, it looks like there is something in the law that only provides DMCA safe harbor to providers that have a policy of terminating accounts of repeat infringers. I'm still not sure if an ISP would even need that safe harbor though.

This was what GFiber appeared to be doing until it sold out to private equity. I got about 60 DMCA notice emails about torrents that never reached seeding state. About 25% of them were false accusations with wrong titles unrelated to activity by anyone on my network.