How do you say "My (noun) broke" in French?
Are you a native speaker? Well, I'm not one but I think in this case we should use the verb "être":
"Ma voiture s'est cassée", my car broke, not specifically by someone.
To me, it feels like if you use "avoir" it means that someone broke something, like "Il a cassé mon coeur".
Since I'm not a native speaker, I'm not sure. Let me know if I'm wrong, it's just what it feels like to me.