It's not legally theft if Google makes a decision to start paying party B instead of party A.
You're choosing to let YouTube publicly host the video until further notice, and in exchange they agree to pay you whatever cut of ad revenue they deem appropriate. There's no question that under the terms you agree to, they can demonetize your videos at will. And if they also see fit to start paying somebody else when your videos get played, that's not something you have legal standing to complain about.
What it probably is, is fraud on the part of whoever's falsely claiming to Google that they have a copyright interest.
You're choosing to let YouTube publicly host the video until further notice, and in exchange they agree to pay you whatever cut of ad revenue they deem appropriate. There's no question that under the terms you agree to, they can demonetize your videos at will. And if they also see fit to start paying somebody else when your videos get played, that's not something you have legal standing to complain about.
What it probably is, is fraud on the part of whoever's falsely claiming to Google that they have a copyright interest.