You still have to send a request to the Vpn when you connect to it, your ISP can just block that initial connection, which is unencrypted. The only solution would be to connect to the vpn now and stay connected through net neutrality death 24/7 which is pretty difficult
VPNs just encrypt and tunnel information you send and receive from the Internet, but you still have to activate the VPN which would require a connection that any isp could see