Same thing happened to me yday. I emailed yahoo customer service. No response. I called them today on the number posted here. Got a rep who said I needed to give them my birthdate that I have on my account for tehm to do anything.

Without that , they cannot help. I had set it up so long ago, I dont know what birthdate I gave them, so looks like I have lost my yahoo account to somebody else for good.

need to ask them to disable it so it isnt misused.