Do NOTHING.

ESPECIALLY if you DO recognise the voice.

Vengeance is a dish best served cold

Assume that you won't know the voice - they could be total strangers .......
They didn't give out much information, BUT the phone company DID [apartment No !!!!]
Ask them what THEY intend to do about their lapse ???

I.D. theft is a growing concern, just let this be your intro, with [hopefully] minimum impact. Learn from it, and keep yourself aware of your situation at all times.
But don't let them stop you from being / doing what ever it is YOU need to do, to keep YOUR life as your own. Otherwise the scum win and that is NEVER a good thing.

Their are people here who will never sit with their back to a door in a public place, because that's how you managed to survive long enough to get here I got into some strange habits when in crowded places [malls etc] wallet into front pocket, cell phone into other front pocket, no watch, all pockets that can button up - button them, and a constant movement of head to keep as much of the masses in 'view' [spatial awareness]. Mind you, I also shred EVERYTHING that has my address on it before it goes into the bin, AND I never leave empty cardboard boxes out by the bin either [why advertise that you've bought something ??

You don't HAVE to be as paranoid as me
But SOME paranoia helps.

Security : It's not ALL about PC's :

Nowaday it's ID theft :
Tomorrow ?

Who knows.

Luck to you ..........