Is that something YouTube does? I was under the impression demonitized videos had no ads of any kind. As opposed to the copyright system rules where you will get ads but the revenue is diverted to someone else instead.
To clarify - often videos will have ads on them prior to being demonetized. My understanding is that when this happens, YT keeps all of the ad revenue and the creator sees none. Over time this is a lot of money I am sure.