If a hacker has hacked your Facebook or Instagram account and knows your information through Facebook or Instagram then using a VPN to hide your real IP address won't do anything to protect you from the hacker.
If your Facebook or Instagram account was hacked you need to secure it again by changing passwords.
Then using a VPN can help protect you a little bit by hiding your IP address from that hacker but it won't protect you much.
Still using a VPN can stop websites from tracking your location etc.