A few years ago I was torrenting a large collection of games without a VPN. It wasn't subtle at all. My internet connection kept getting slower and slower. I had to repeatedly restart the download for it to finish.

Afterwards my internet was totally busted. I called my ISP to complain. They walked me through some debugging but I could tell it was bullshit. Suddenly my internet started working. After I got off the phone, I got an automated text from the ISP that my internet had been reactivated.

So yeah. They can/will block your internet for downloading stuff. Use a VPN.