Hacked iCloud makes my iphone useless?

So lately my icloud has been hacked, the password & security questions have been changed.

Now i get a popup to enter my icloud password (wich i don't have anymore obviously) every 5 minutes.

I made a new icloud account, but my phone won't allow me to log out of my previous account without entering the password.

Now what am i supposed to do? Is my phone useless now?...