How can I stop getting notifications telling me that some AirPods are moving with me?

I inherited some AirPods. So I didn't buy them, and they were originally paired with a different device.

I have unpaired it from every possible device owned by the original owner.

I have unpaired and repaired on my phone.

Still, I get the notifications telling me that some AirPods are moving with me.

I would really like that to stop.

Any clues? What obvious thing have I not done?

[Re-Titled by Moderator]