A VPN hides your IP address but the VPN only hides your IP address to the websites you're visiting but the VPN does not hide your real IP address from your ISP.
When you have internet service you have an IP address assigned to your modem through the ISP and that ISP can see your real IP address and knows your real IP address at all times.
So if you download something illegal or stream videos illegally then the ISP will be able to know it's you so I would advise against streaming anything illegally because if caught you can be fined or even thrown in jail over it.
Most times though if you stream something illegally then the website owner will be the one in trouble instead of the person downloading or streaming the stuff from the illegal website.
That is unless you download something such as child porn etc then both the website owner and anyone who knowingly or purposely browsed that website or downloaded said illegal material can and will be charged with the crime.