Horror movie about demons disguised as people

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I watched a horror movie many years ago that i’d like to revisit. I don’t remember the name or the cast, just the basic plot and some specific scenes that impacted me most.
It’s a horror/thriller movie that had a female main character and there were these demons that looked and behaved like humans trying to get her for some reason. I remember this specific scene where she was in her house and a dog appeared outside her door trying to get in, she wouldn’t let it come in afraid it would be one of those demons. Then the dog turns into some kind of slime/paste and goes in through the mail entrance at the door and attacks the mc. She runs for some time and that thing was indestructible, everytime she would fight it it would turn into this paste and regenerate (???). She eventually escapes it.

Another thing i remember is that these “demons”, while disguised as humans, could be exposed by playing a certain music (classical/piano music i think) and when they hear it they would get super triggered and lash out. When the mc is introduced to the organization responsible to fight these creatures, she finds out that Mozart (or Bethoven, i cant remember) was actually a member of the society a long time ago, and was the one who created these melodies that exposed the demons.

I really don’t remember anything else that might be useful and i’m sorry if this sounds confusing (i’m sure it does). Hope someone can help me out.

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