People are using this system intentionally as a scam. Recently, I tried uploading a video which had video game music in the background, and youtube flagged a copyright claim on behalf of someone who made a remix of the original song. I did not have a license to use the song, so that's fair, but my choices were either to drop my video or run ads that give money to someone who wasn't even the owner of the song I was trying to use.
There was no avenue for recourse, or to report the person who was fraudulently making claims.
Can you reach out to the original composer of the game music? They would likely care about the bogus claims. Particularly if it is a smaller studio. It’s not a great solution, but it might work.
Im not excusing what happened, but was the remix author actually making claims? Or did they just add a song to ContentID’s database? If it’s the former, that’s despicable and (almost certainly) illegal. If it’s the latter, it’s not their fault, but Google’s for having an overzealous system.
There was no avenue for recourse, or to report the person who was fraudulently making claims.