If a server is VAC protected, you can get banned in it.
Your cheat you used probably was detected.
Have you ever cheated prior to this since VAC bans can be delayed.
Regarding VACNet, it is possible but it would've had to auto-banned you especially since you didn't cheat in an official game server, thus being unable to send you to Overwatch.
What does the ban say when you launch CS:GO?