what do I do about my neighbors?

if I’m being honest, it sounds like they’re abusing their kid. there is constant loud banging, screaming, baby crying and screaming. I think there is a difference between a child that is crying because it needs something, or a child that is screaming because it’s scared. it’s to the point that this has happened everyday for months now. It’s not just little bangs it’s very loud and I can’t help but feel like something bad is happening. We called the police a few months back but unfortunately nothing was done. it’s gotten much much worse than the night that we called but my fiancé’s mom who was a social worker said that we shouldn’t call again unless we have solid proof. I also don’t know if this is very wrong but right now the child, I’m guessing is younger than 1 1/2-2 years old, is sitting outside on a balcony 2 stories up, completely by himself. Should I do something? Should I call someone? I only say this because I’m concerned for that child’s safety. thanks for any input